'nimble install nimble' fails looking for: 'system.nim' file
Hi

I upgraded to Nim 1.2.2, building from the source download archive obtained from the nim-lang web downloads page, which went fine. I removed my previous install first, that was also located in `~/.nimble`.

I then tried to update `nimble` to the latest version using:  `nimble install nimble` but this fails looking for a file `system.nim` that does not exist in my Nim installation. 

A secondary issue is that it looks like the version of `nimble` included with the Nim build is the same as the one it is trying to upgrade too (ie v0.11.4) as well - not sure if this is a feature :)

Additional informaiton below.

Thanks

Simon

```
simon@alienmoons:~$ nimble -v
nimble v0.11.4 compiled at 2020-06-21 07:17:02
git hash: couldn't determine git hash
simon@alienmoons:~$ nimble install --verbose nimble
    Reading official package list
Downloading https://github.com/nim-lang/nimble using git
    Cloning latest tagged version: v0.11.4
     Error: Could not read package info file in /tmp/nimble_9086/githubcom_nimlangnimble/nimble.nimble;
        ...   Reading as ini file failed with: 
        ...     Invalid section: .
        ...   Evaluating as NimScript file failed with: 
        ...     Error: cannot open '/home/simon/.nimble/nim/lib/system.nim'
        ... printPkgInfo() failed.
simon@alienmoons:~$ cd .nimble/
simon@alienmoons:~/.nimble$ find . -name "system.nim" -print
simon@alienmoons:~/.nimble$ ls nim/lib/
arch/  deprecated/    genode/      impure/  nintendoswitch/  posix/  std/     windows/
core/  experimental/  genode_cpp/  js/      packages/        pure/   system/  wrappers/
simon@alienmoons:~/.nimble$ ls nim/lib/system/
mm/
simon@alienmoons:~/.nimble$ ls nim/lib/system/mm/
simon@alienmoons:~/.nimble$ nim --version
Nim Compiler Version 1.2.2 [Linux: amd64]
Compiled at 2020-06-16
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: be34b5abe23e027b71a3a9da67037aac7afea6bc
active boot switches: -d:release
simon@alienmoons:~/.nimble$ 
```
