Travis-CI needs update for JDK 6?

at https://github.com/scala/scala-parser-combinators/pull/179 , it looks like whatever we're doing to get JDK 6 on Travis-CI isn't working anymore

someone might like to take a look at what https://github.com/scala/scala-xml/blob/master/.travis.yml is doing and see if it needs to be applied here, or what