Domain Fix to Account for Github Security Patch

On April 25, 2014, Github initiated the following security patch (https://developer.github.com/changes/2014-04-25-user-content-security/). Unfortunately, the redirect from github.com githubusercontent.com was failing during our instance of chef provisioning for a vagrant instance. Although we implemented a work around in our provisioning process, it seems like rvm should update appropriate instances of github.com to githubusercontent.com to accommodate the Github security patch. This fork contains the necessary updates to accomplish this.