choosenim destructive: upon restoring it, it destroys some binaries
## current behavior
```
choosenim Nim1
nimble install -y nimble
nimble -v
nimble v0.12.0 compiled at 2020-11-14 00:18:47
git hash: 8f7af860c5ce9634af880a7081c6435e1f2a5148

choosenim Nim2
    Prompt: Symlink for 'nimble' detected in '/Users/timothee/.nimble/bin'. Can I remove it? [y/N]
    Answer: y
    Removed symlink pointing to ../pkgs/nimble-0.12.0/nimble
  Installed component 'nimble'
   Switched to Nim (/Users/timothee/git_clone/nim/Nim_prs)
nimble -v
nimble v0.12.0 compiled at 2020-11-10 20:01:12
git hash: 8f7af860c5ce9634af880a7081c6435e1f2a5148

choosenim Nim1
nimble -v
nimble v0.11.0 compiled at 2020-04-04 14:23:52
git hash: 4007b2a778429a978e12307bf13a038029b4c4d9
```

## expected behavior
upon restoring `choosenim Nim1` I'd expect to get back `nimble v0.12.0` 

