The Ruby stack now supports JRuby 1.7.12 in 2.0.0 (experimental), 1.9.3 mode. There were issues building 1.8.7 mode, so that was left out and we’re working with the JRuby team to fix build issues in 1.7.13+.
To use JRuby 1.7.12 in Ruby 1.9.3 mode, add this to your
ruby '1.9.3', :engine => 'jruby', :engine_version => '1.7.12'
ruby value depending on the mode you wish to use.
The JRuby release notes can be found here.