Update Gruntfile.js

Run 'grunt ionicSass' to update your ionic.css file.
Allows you to make changes to ionic's variables.scss file
Merge commit '4e958377b35eac49c41399a98946106c99229683'

* commit '4e958377b35eac49c41399a98946106c99229683':
  Update Gruntfile.js