Added PHP 5.6 and HHVM to travis.yml
Merge pull request #2 from Nyholm/patch-1

Added PHP 5.6 and HHVM to travis.yml

Thank your for the PR, but please note that you should use firebase/php-jwt going forward.  Since I forked the project they have added composer support.  They also have a travis.yml file but it lacks what this PR adds, so you may want to make the same PR on that project.  Thanks again.