Tell PhantomJS where to look for files

I'm trying to use phantom.openPage to see if we can tell phantom where to look for JS files.
Are you sure this is right? 'Cause I see on [AppVeyor](https://ci.appveyor.com/project/giakki/uncss/build/113) `Uncaught AssertionError: expected 'UnCSS: could not open c:\\C:\\projects\\uncss\\tests\\selectors\\fixtures\\adjacent.css' to include 'unable to parse'`, two `c:\`. Maybe `path.join` isn't needed here?