Add Rubinius 2.2.1 and 2.1.1 to the Travis build matrix

Travis now provides stable Rubinius releases, this adds 2.2.1 and 2.1.1 to see if some tests need to be fixed. From reading [the docs](http://about.travis-ci.org/docs/user/languages/ruby/#Rubinius) it looks like Travis only has packages since the 2.1.1 release. Maybe also add 2.2.0? 

Refs #1275