Add fix for core.py missing space

[Rtanti]

A space was missing when running conda-unpack --help between unarchiving and Cleans

usage: conda-unpack [-h] [--version]

Finish unpacking the environment after unarchiving.Cleans up absolute prefixes in any remaining
files

optional arguments:
  -h, --help  show this help message and exit
  --version   Show version then exit```
Now it should be

$ conda unpack --help
usage: conda-unpack [-h] [--version]

Finish unpacking the environment after unarchiving. Cleans up absolute prefixes in any remaining
files

optional arguments:
  -h, --help  show this help message and exit
  --version   Show version then exit```

[anaconda-issue-bot]

We require contributors to sign our Contributor License Agreement, and we don't have one on file for @Rtanti. In order for us to review and merge your code, please e-sign the PDF at https://conda.io/en/latest/contributing.html#conda-contributor-license-agreement. We then need to manually verify your signature. We will ping the bot to refresh the PR status when we have confirmed your signature.

[Rtanti]

Resolves #215

[kenodegard]

@anaconda-issue-bot check

[kenodegard]

@Rtanti thanks!