Disable node 8 tests on Travis
Disable node 8 tests on Travis

- For some unknown reason Travis is failing on Node 8 tests due to some
problem with babel. This doesn't happen locally with the exact same
version of Node, so this just disables the tests until they can run on
Travis.

tgriesser/bookshelf,tgriesser/bookshelf,bookshelf/bookshelf,bookshelf/bookshelf