Allow JRuby to run tests 

In an attempt to track down the `ActionView::Template::Error (Illegal replacement)` transcoding error in JRuby, I updated sqlite gem to be platform specific:

    gem "sqlite3", ">= 1.3.4", platform: :ruby
    gem "jdbc-sqlite3", ">= 3.7.2",  platform: :jruby
    gem "activerecord-jdbc-adapter", ">= 1.2.8",  platform: :jruby

 The one caveat for this to work is these gems have to be moved to the Gemfile and out of the gemspec. 

Issue #156