Nimarchive cannot overwrite existing extraction?
Getting this error which makes choosenim unusable:

```
PS C:\Users\morfe\projects\stardust> choosenim 1.2.0
      Info: C:\Users\morfe\.choosenim\downloads\dlls.zip already downloaded
 Extracting dlls.zip
     Error: Unable to extract. Error was 'Cannot create a file when that file already exists.
        ... '.
```

The extraction is into nimble bin dir (the same as returned by ``choosenim --getNimbleBin``). So it fails because it's trying to extract DLLs that are already there...

Steps to repro:

* Rename libeay32.dll to libeay32.dll.old (or any other dll installed by choosenim)
* Run `choosenim 1.2.0`

You will see that error.