Use `http://rubygems.org` instead of `https://rubygems.org`.

See https://github.com/rubygems/rubygems.org/issues/615
    https://github.com/livingsocial/rearview/commit/c4e05ec
Merge pull request #127 from seomoz/phs/use-http-rubygems

Use `http://rubygems.org` instead of `https://rubygems.org`.