Treat missing CONTENT_TYPE as an unhandled content type
Update travis.yml JRuby/Rbx config.

Allow rbx failures due to
https://github.com/travis-ci/travis-ci/issues/2230
Update Travis Ruby 2.1 config

Specify as 2.1, not 2.1.0 per
https://github.com/travis-ci/travis-ci/issues/2220