[travis-ci] exclude all of jruby-head with openjdk6
[travis-ci] exclude all of jruby-head with openjdk6
jruby/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack,jhstatewide/jruby-rack,jruby/jruby-rack