Travis - Ruby 2.1.0, fix Rubinius build

1. Added Ruby 2.1.0 as a non-allowed failure, as this is now a released Ruby
2. Fixed the rbx build by adding required gems, fixing the label in the .travis.yml

On a related note, there definitely appears to be a transient failure with Ruby 1.9.3 - sometimes it fails, sometimes it succeeds.  Probably requires some investigation.

I'm assuming the JRuby failures are known, based on JRuby being an allowed_failure in the test matrix.

Rubinius now passes reliably, so if desired it can be pulled out of the allowed_failures.