'nbinteract init' bug in binder_spec_from_github_url
'nbinteract init' bug in binder_spec_from_github_url

The implementation of binder_spec_from_github_url was removing all '.git' substrings, which was causing a bug for github pages or any repo with 'git' in the title.
Eg. My repo https://github.com/samlaf/samlaf.github.io was resulting in the spec 'samlaf/samlafhub.io/master' instead of 'samlaf/samlaf.github.io/master'.
This pull request fixes that.
SamLau95/nbinteract,SamLau95/nbinteract,SamLau95/nbinteract