Remove deprecated Grunt dependency

`grunt.util._` [is deprecated](http://gruntjs.com/blog/2013-11-21-grunt-0.4.2-released) and will be removed in the future. 

Seen here: https://github.com/use-init/init/blob/master/Gruntfile.js#L33

Make LoDash a dependency and use `var _ = require('lodash')` instead.