Use proper clone syntax when cloning.

Summary:
I guess git://... works, but it doesn't allow for pushing.  We want
git@... instead.

Test Plan:
Manually ran
   git clone git@github.com:Khan/kiln-review
and had it work successfully.

Reviewers: benkomalo, alpert

Reviewed By: benkomalo

Differential Revision: http://phabricator.khanacademy.org/D2260