Upgrade to PhantomJS 2.x

[notmessenger]

https://www.npmjs.com/package/phantomjs is a NPM wrapper around phantomjs binary. The version of phantomjs it installs is in https://github.com/Medium/phantomjs/blob/master/lib/phantomjs.js

TravisCI uses phantomjs version 1.9.8 (travis-ci/travis-ci#3225), same as npm phantomjs