changes current browser to phantomjs

Hey All,

small tweak here, I switched over your test runner from Firefox (booo) to PhantomJS (yay)!  Seems the only reason it was listed as being required was the TravisCI only has firefox (hence the comment).

Luckily TravisCI has PhantomJS preinstalled (see below)

http://about.travis-ci.org/docs/user/gui-and-headless-browsers/

small change as I work through refactoring the tests on #583