List files via standard grunt processing for newer compatibility

[grayside]

After some time researching the issue (by way of #23) I learned that grunt's core handling of files configuration already produces a flattened list of all files for task processing. The grunt-newer plugin takes advantage of that behavior to then strip down that list of files to only those that meet it's criteria to move forward.

This change aligns grunt-phpcs with this pipeline and allows grunt-newer to work.