Change phantom.args to system.args

[MaxPleaner]

phantom.args is deprecated (link)[http://phantomjs.org/api/phantom/property/args.html)

The readme just needed to be updated.

For me, I just followed the default install instructions. I'm on Ruby 2.2.0

The fix for me was to use system.args instead.

Unfortunately Phantom can be hard to debug since there are no error traces whatsoever.

Thanks for the useful gem by the way