Make compatible with Rails 4.1 and Rails 4.2

:bullettrain_side::arrow_upper_right: 

### Description
 - Add 4.1 and 4.2 gemfiles and configure Travis
 - Add actionview to 4.2 gemfile because it's not autoloaded by actionpack
 - Fix testhelper to be compatible with minitest 5 and rails >= 4.1
 - Fix spec for 4.2 because Symbol is casted into String

### Steps to merge
 - [ ] :+1: of the team
Since this gem is tested for JRuby we actually can't commit the gemfile.lock because some gems are platform dependent ... I tried (which is the cause of the change) but failed hard ...