[build] use gulp instead of grunt

use gulp instead of grunt

TODO
* [ ] Bump
* [ ] Karma Test fails

Need help to fix the karma run. @gr2m 

    PhantomJS 1.9.7 (Mac OS X) ERROR
      ReferenceError: Can't find variable: sinon
      at /var/folders/69/d7_81n851vd7tr6_48x80mmw0000gn/T/karma-browerify.js:5680

Just add karma to the karma.files?