Rubinius fixes.

Rubinius 2.1.1 is already passing the test suite, although it was failing on picking up unicorn, since the Gemfile was excluding it.
Also test against  the latest version on Travis, `rbx` alone still installs a very old 2.0.0.rc2 build.

You might want to delete it from the allowed failures, but it's up to you. ;)
Thanks.