Update dependencies / Remove deprecated utilities

* Updated dependencies and devDependencies
* Replaced [grunt.util._](http://gruntjs.com/api/grunt.util#grunt.util._).each with [Array.forEach](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach) and [grunt.util.async](http://gruntjs.com/api/grunt.util#grunt.util.async) with [npm's async](https://npmjs.org/package/async), because [they are deprecated](http://gruntjs.com/api/grunt.util#external-libraries).