Installer Script Fails -- Symlink
## Expected behavior, english is required

The installer script should always run. 

OR 

`git clone` on the repo should succeed.

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

Run the install script in a directory that is backed by a file system that does not support links (e.g., FAT). This seems to be the case on the Github actions MacOS runner (see https://github.com/ssbanerje/dotfiles/runs/3581503715?check_suite_focus=true#step:5:750). 

## Error
```
        /######                                     /##    /##/##             
       /##__  ##                                   | ##   | #|__/             
      | ##  \__/ /######  /######  /####### /######| ##   | ##/##/######/#### 
      |  ###### /##__  ##|____  ##/##_____//##__  #|  ## / ##| #| ##_  ##_  ##
       \____  #| ##  \ ## /######| ##     | ########\  ## ##/| #| ## \ ## \ ##
       /##  \ #| ##  | ##/##__  #| ##     | ##_____/ \  ###/ | #| ## | ## | ##
      |  ######| #######|  ######|  ######|  #######  \  #/  | #| ## | ## | ##
       \______/| ##____/ \_______/\_______/\_______/   \_/   |__|__/ |__/ |__/
               | ##                                                           
               | ##                                                           
               |__/                                                           

                      version : .8.0-dev      by : spacevim.org             

[➭] Trying to clone SpaceVim
Cloning into '/Users/runner/.SpaceVim'...
error: unable to create symlink doc/SpaceVim.cnx: File name too long
fatal: unable to checkout working tree
warning: Clone succeeded, but checkout failed.
You can inspect what was checked out with 'git status'
and retry with 'git restore --source=HEAD :/'

[✘] Failed to clone SpaceVim
Error detected while processing command line:
E: Unknown function: dein#install
remote/host: generated rplugin manifest: /Users/runner/.local/share/nvim/rplugin.vimError detected while processing command line:
```

## Potential Solution

Could the symlink be put in by the installer script or by the first execution of vim, if the underlying file system supports it.
