Adding travis testing for multiple java versions

Status: https://travis-ci.org/cldwalker/pedestal/builds/5714062

To enable this on travis, someone has to log into pedestal's github account via travis.

Some additional considerations if pulling this in:

* Do we want to switch completely to travis or have CIs for this repo?
* Add travis status icon to readme
* Document $LEIN_CMD i.e. if anyone calls "lein" as I did in an integration test it must also take $LEIN_CMD
* Add travis to samples