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
might work when run with `bundler_args: ""` <-> locally I never had to
remove a Gemfile.lock to make jruby work

On Wed, Oct 29, 2014 at 2:07 AM, Pierre Schambacher <
notifications@github.com> wrote:

> In .gitignore:
>
> > @@ -7,4 +7,4 @@ doc
> >  .yardoc
> >  .bundle
> >  pkg
> > -gemfiles/*.lock
> > +gemfiles/*.gemfile.lock
>
> 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 ...
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/zendesk/property_sets/pull/45/files#r19525836>.
>