add jruby test
Fix warning warning libjffi-1.2.so on < JRuby 1.7.3

[JRuby Issue](https://github.com/jruby/jruby/issues/899). We need to use
an older JDK for JRuby 1.7.3 and lower.
update changelog
Merge pull request #168 from heroku/jdk_u40_update

Fix warning warning libjffi-1.2.so on < JRuby 1.7.3