Specify Github API version explicitly

Please see http://developer.github.com/v3/versions/ . From March 15, 2014 the Github API default will switch to `v3` from `beta`. This will break a few things in RCloud, for which the detailed list is here. http://developer.github.com/v3/versions/#differences-from-beta-version 

The proposed change ensures that we explicitly provide `beta` as a specific version until we are ready to move to `v3`.