Allow Travis to silently fail on HHVM. The issue it is currently failing is because of a enhancement to the Doctrine DBAL for HHVM that hasn't been implemented into a release yet (it's pending DBAL 2.4.0). Unfortunately, the DoctrineBundle, and even the dev-master branch of the Doctrine Bundle, hasn't been updated to allow for the dev-master branch of this version of the Doctrine DBAL. See https://github.com/doctrine/dbal/pull/373