Fix dangling commas

Hi, I'd like to first say thanks for writing this very very cool plugin.

I noticed today as I was skimming your grunt file(bear with me, today is my first day working with grunt) that there was inconsistent use of commas after the last property:value(key:value?) in some option definitions.  I was unsure if it was deliberate or a mistake. I also noticed this problem in the readme.md  If I am mistaken please forgive my blunder and kindly inform me the purpose of having dangling commas. I would very much appreciate it. Thanks for your time.