fixed dangling commas

Hi, 
First I'd like to thank you immensely for creating this really really cool plugin. This has been immensely helpful in my learning process of grunt.  As I was scanned your code and example code I noticed that there where dangling commas used in object definitions.  I was not sure if this was deliberate or not due to style inconsistencies from the files that I saw.  I am unsure of the usefulness of these dangling commas. I am guessing so you do not have to guess where to put commas and where not to?  If I am mistaken please forgive me for my blunder, I am new to the JS world.  Thanks for your time.