Test that an exception is raised on no CONTENT_TYPE
Treat missing CONTENT_TYPE as an unhandled content type
Update travis.yml JRuby/Rbx config.
Update travis.yml Ruby 2.1 config

Specify as 2.1, not 2.1.0 per
https://github.com/travis-ci/travis-ci/issues/2220
Faster parsing of content_type from env

see
https://github.com/whitequark/rack-utf8_sanitizer/pull/10#discussion_r12441827
Merge pull request #10 from whitequark/handle_no_content_type

Handle no content type