Make nib optional

[sheriffderek]

http://visionmedia.github.io/nib/
vs
http://tj.github.io/nib/
?

I'm not sure what the story with Nib is these days, since autoprefixer, I've never used it. Do people still use it? Is there a flag or config to remove its inclusion?

[shvaikalesh]

Fixed in a3dd383. Thanks @sheriffderek.