use git:// instead of http:// for centos

I'm experimenting with CentOS 6.5 in my work environment, and for some reason git hangs on the http:// protocol in the setup script.

Since I've always seen these kinds of urls specified as git:// instead of http:// anyway, I figured I'd give that a try and it worked a treat.  I feel confident it wouldn't cause problems in any other environment, so I'm submitting a pull request.

Thanks.