Updated Travis-Ci ruby matrix to include JRuby
Updated Travis-Ci ruby matrix to include JRuby

* Since I switched the project to JRuby for local development,
  I added JRuby 1.7.1 to the .travis.yml file. This means we now
  cover Ruby 1.9.2, 1.9.3, and JRuby 1.7.1. Adequate coverage so far.

dtf-gems/dtf,dtf-gems/dtf,ddd/dtf,ddd/dtf