Add Ruby 2.1.0 and rbx to .travis.yml.  Add required Rubinius gems.

1. Added Ruby 2.1.0 to Travis
2. Added gems required for Rubinius to Gemfile
3. Added rbx label to .travis.yml, but allowed failures

I'm seeing a couple of failures under Rubinius that are occurring because a process is still alive after stop_process is called.  Otherwise rbx runs green.