travis: only run the alternate Gemfile with MRI 2.1
travis: only run the alternate Gemfile with MRI 2.1

Ruby 2.2(.2+) don't need the alternate Gemfile, so don't use that.

While at it also simplify Travis tests specifying JDK just for JRuby
and avoid installing Bundler since 1.12 is already good enough.

3scale/3scale_ws_api_for_ruby