Should fix the travis errors

This should fix all travis errors
Details:
* `.travis.yml` travis has a bug with `rbx` "_When using Rubinius, there's currently an issue with selecting the correct version in RVM in our build environment, but only when specifying rbx as your version. As a workaround, specify rbx-2 instead._"

* `Gemfile` checking if the rails  environment is either master or more than 4.1(regex) to require minitest 5.1 otherwise keep the old minitest version

* `slim_test.rb`: there was a problem with rails 3.1.x and jruby-mode19 when streaming


* `gitignore`: I'am using rubymine just added the config folder to gitignore

Can you find out why JRuby fails? I would prefer to have the test activated for JRuby and fix then the real problem.