use selenium instead of talking directly to phantom

Thanks to @jason0x43 for pointing out the bug that prevents Intern 2 from talking to PhantomJS directly.

Brings `intern.js` in line w/ [wiki page](https://github.com/theintern/intern/wiki/Using-Intern-with-PhantomJS) and instructs user to start Selenium instead of PhantomJS.

This got it working in my environment.

Resolves #6