Minor nitpick on directory selection

[equwal]

This line should not be able to have two dashes when I clone a thing:

$ gh roswell roswell
Cloning into '/home/l33t-hax0r/src//github.com/roswell/roswell'...

Reproduction:

set -x GH_BASE_DIR /home/ur-mum/src/ # leave final slash

This is a non-breaking bug.

[equwal]

Closing, see the pull request #45.