Global conceal priority is falsely lower than indentLine
<!-- bug reporting without issue template will be closed automatically -->

## Expected behavior, english is required
I expect that Global conceal setting is able to override the settings by `indentLine` via the following settings:

```vim
" The first method:
set conceallevel=2

" The second method:
let g:markdown_syntax_conceal = 0
```

Currently, none of these methods works to disable markdown completely.

**So, please fix it to make sure the global conceal setting works correctly.**

## The reproduce ways from Vim starting (Required!)

For example, add the following settings into your `init.vim` to disable conceal completely:

```vim
set conceallevel=0

" Or you can try this
let g:markdown_syntax_conceal = 0
```

However, conceal level still is set to `2` by `indentLine`:

You may get the same result using [`:verbose set conceallevel? concealcursor?`](https://github.com/SpaceVim/SpaceVim/issues/2033#issuecomment-417756611)
![image](https://user-images.githubusercontent.com/12933851/118460736-90771000-b72f-11eb-9fed-885d0bdd06fc.png)

## How can I make it work

Use indentLine settings to override global conceal:

```vim
" set conceallevel=0
" let g:markdown_syntax_conceal = 0
let g:indentLine_setConceal = 0
```

So, it works.
![image](https://user-images.githubusercontent.com/12933851/118462583-67f01580-b731-11eb-8873-207c509fcbb3.png)


## Debug info

Please press <kbd>SPC h I</kbd>, debug info will be put into clipboard, then paste all content below.

<details>
<summary>Expand/Collapse</summary>

```vim
SpaceVim layers:

+ VersionControl:           loaded          https://spacevim.org/layers/VersionControl/
+ autocomplete:             loaded          https://spacevim.org/layers/autocomplete/
- chat:                 not loaded          https://spacevim.org/layers/chat/
+ checkers:                 loaded          https://spacevim.org/layers/checkers/
- chinese:              not loaded          https://spacevim.org/layers/chinese/
+ colorscheme:              loaded          https://spacevim.org/layers/colorscheme/
+ core#banner:              loaded          https://spacevim.org/layers/core/banner/
+ core#statusline:          loaded          https://spacevim.org/layers/core/statusline/
+ core#tabline:             loaded          https://spacevim.org/layers/core/tabline/
+ core:                     loaded          https://spacevim.org/layers/core/
- cscope:               not loaded          https://spacevim.org/layers/cscope/
- ctrlp:                not loaded          https://spacevim.org/layers/ctrlp/
- ctrlspace:            not loaded          https://spacevim.org/layers/ctrlspace/
- debug:                not loaded          https://spacevim.org/layers/debug/
- denite:               not loaded          https://spacevim.org/layers/denite/
+ edit:                     loaded          https://spacevim.org/layers/edit/
- exprfold:             not loaded          no exists
- floobits:             not loaded          https://spacevim.org/layers/floobits/
- foldsearch:           not loaded          https://spacevim.org/layers/foldsearch/
+ format:                   loaded          https://spacevim.org/layers/format/
- fuzzy:                not loaded          no exists
+ fzf:                      loaded          https://spacevim.org/layers/fzf/
- games:                not loaded          no exists
- git:                  not loaded          https://spacevim.org/layers/git/
- github:               not loaded          https://spacevim.org/layers/github/
- gtags:                not loaded          https://spacevim.org/layers/gtags/
- incsearch:            not loaded          no exists
- indentmove:           not loaded          no exists
- japanese:             not loaded          https://spacevim.org/layers/japanese/
- lang#WebAssembly:     not loaded          https://spacevim.org/layers/lang/WebAssembly/
- lang#actionscript:    not loaded          https://spacevim.org/layers/lang/actionscript/
- lang#agda:            not loaded          https://spacevim.org/layers/lang/agda/
- lang#asciidoc:        not loaded          https://spacevim.org/layers/lang/asciidoc/
- lang#aspectj:         not loaded          https://spacevim.org/layers/lang/aspectj/
- lang#assembly:        not loaded          https://spacevim.org/layers/lang/assembly/
- lang#autohotkey:      not loaded          https://spacevim.org/layers/lang/autohotkey/
- lang#batch:           not loaded          https://spacevim.org/layers/lang/batch/
+ lang#c:                   loaded          https://spacevim.org/layers/lang/c/
- lang#chapel:          not loaded          https://spacevim.org/layers/lang/chapel/
- lang#clojure:         not loaded          https://spacevim.org/layers/lang/clojure/
- lang#coffeescript:    not loaded          https://spacevim.org/layers/lang/coffeescript/
- lang#crystal:         not loaded          https://spacevim.org/layers/lang/crystal/
- lang#csharp:          not loaded          https://spacevim.org/layers/lang/csharp/
- lang#d:               not loaded          https://spacevim.org/layers/lang/d/
- lang#dart:            not loaded          https://spacevim.org/layers/lang/dart/
- lang#dockerfile:      not loaded          https://spacevim.org/layers/lang/dockerfile/
- lang#e:               not loaded          https://spacevim.org/layers/lang/e/
- lang#eiffel:          not loaded          https://spacevim.org/layers/lang/eiffel/
- lang#elixir:          not loaded          https://spacevim.org/layers/lang/elixir/
- lang#elm:             not loaded          https://spacevim.org/layers/lang/elm/
- lang#erlang:          not loaded          https://spacevim.org/layers/lang/erlang/
- lang#extra:           not loaded          https://spacevim.org/layers/lang/extra/
- lang#factor:          not loaded          no exists
- lang#fennel:          not loaded          https://spacevim.org/layers/lang/fennel/
- lang#forth:           not loaded          no exists
- lang#fortran:         not loaded          https://spacevim.org/layers/lang/fortran/
- lang#foxpro:          not loaded          https://spacevim.org/layers/lang/foxpro/
- lang#fsharp:          not loaded          https://spacevim.org/layers/lang/fsharp/
- lang#go:              not loaded          https://spacevim.org/layers/lang/go/
- lang#goby:            not loaded          https://spacevim.org/layers/lang/goby/
- lang#gosu:            not loaded          https://spacevim.org/layers/lang/gosu/
- lang#graphql:         not loaded          https://spacevim.org/layers/lang/graphql/
- lang#groovy:          not loaded          https://spacevim.org/layers/lang/groovy/
- lang#hack:            not loaded          https://spacevim.org/layers/lang/hack/
- lang#haskell:         not loaded          https://spacevim.org/layers/lang/haskell/
- lang#html:            not loaded          https://spacevim.org/layers/lang/html/
- lang#hy:              not loaded          https://spacevim.org/layers/lang/hy/
- lang#idris:           not loaded          https://spacevim.org/layers/lang/idris/
- lang#io:              not loaded          https://spacevim.org/layers/lang/io/
- lang#ipynb:           not loaded          https://spacevim.org/layers/lang/ipynb/
- lang#j:               not loaded          https://spacevim.org/layers/lang/j/
- lang#janet:           not loaded          https://spacevim.org/layers/lang/janet/
- lang#java:            not loaded          https://spacevim.org/layers/lang/java/
+ lang#javascript:          loaded          https://spacevim.org/layers/lang/javascript/
- lang#json:            not loaded          no exists
- lang#julia:           not loaded          https://spacevim.org/layers/lang/julia/
- lang#kotlin:          not loaded          https://spacevim.org/layers/lang/kotlin/
- lang#lasso:           not loaded          https://spacevim.org/layers/lang/lasso/
+ lang#latex:               loaded          https://spacevim.org/layers/lang/latex/
- lang#lisp:            not loaded          https://spacevim.org/layers/lang/lisp/
- lang#livescript:      not loaded          https://spacevim.org/layers/lang/livescript/
+ lang#lua:                 loaded          https://spacevim.org/layers/lang/lua/
+ lang#markdown:            loaded          https://spacevim.org/layers/lang/markdown/
- lang#matlab:          not loaded          https://spacevim.org/layers/lang/matlab/
- lang#moonscript:      not loaded          https://spacevim.org/layers/lang/moonscript/
- lang#nim:             not loaded          https://spacevim.org/layers/lang/nim/
- lang#nix:             not loaded          https://spacevim.org/layers/lang/nix/
- lang#ocaml:           not loaded          https://spacevim.org/layers/lang/ocaml/
- lang#pact:            not loaded          https://spacevim.org/layers/lang/pact/
- lang#pascal:          not loaded          https://spacevim.org/layers/lang/pascal/
- lang#perl:            not loaded          https://spacevim.org/layers/lang/perl/
- lang#php:             not loaded          https://spacevim.org/layers/lang/php/
- lang#plantuml:        not loaded          https://spacevim.org/layers/lang/plantuml/
- lang#pony:            not loaded          https://spacevim.org/layers/lang/pony/
- lang#povray:          not loaded          https://spacevim.org/layers/lang/povray/
- lang#powershell:      not loaded          https://spacevim.org/layers/lang/powershell/
- lang#processing:      not loaded          https://spacevim.org/layers/lang/processing/
- lang#prolog:          not loaded          https://spacevim.
```
</details>

## Related Issue
https://github.com/SpaceVim/SpaceVim/issues/2531
https://github.com/SpaceVim/SpaceVim/pull/2298
https://github.com/SpaceVim/SpaceVim/issues/3245
https://github.com/SpaceVim/SpaceVim/issues/2033