Get builds passing reliably on Travis

It looks like the coffee#1.7.x bug surfacing on travis will take some fanangaling, and since there's serious intent to migrate to pure js, I don't think it hurts anyone to pin coffee at 1.6.x.

This PR prevents the JDK6 regression experienced earlier this week, and will surface intelligible errors when JDK8 gets rolled out to over the next few months.

The project is now rebuilt by the CI server on every push, but uses my personal fork of closure-library to do this. I do not intend to take the compatibility branch in my fork down in the near future, but when interdependencies like these start surfacing it can be an indication that it's time for a github organization.