Update Gemfile and specs so that everything runs under JRuby

1. Added some platforms restrictions to the Gemfile, so JRuby incompatible gems are not required when using JRuby
2. Blocked out Objectspace related specs under JRuby
3. Changed a failing step in the batch_action_steps.rb

I'm not really sure why I had to make change #3.  The original test and the changed test should be identical, but the former was failing under JRuby.  With the change it passes.  If anyone has any insight, that would be great.

Also, it's likely possible to re-enable Yard on JRuby - I just disabled it entirely because I didn't want to search for and test a JRuby and Yard compatible Markdown parser.