Travis updates - Ruby 2.1.0, get Rubinius running

1. Added Ruby 2.1.0 to .travis.yml.
2. Added Rubinius gems to gemfiles, so Rubinius build runs.
3. Replace 'rbx-18mode' and 'rbx-19mode' with the updated 'rbx' label

Rubinius runs, but it has a couple of spec failures.  Ruby 2.1.0 specs run green.