Run Tests against JRuby master

Many of the failing tests in rails test suite fail because of missing encoding support, example #11739


And according to recent announcement, lot of encoding issues have been fixed in current master.  http://ruby.11.x6.nabble.com/Big-encoding-patches-landed-on-master-td4993719.html


So lets test against JRuby master & incase there are still bugs. it would be easier to report them to JRuby.