Update Grunt plugins / Fix JSHint setting

* I updated devDependencies of this project and fixed JSHint setting.
  * Now there is no need to set the "ES5" option explicitly. (cf. [JSHint 2.0.0](http://www.jshint.com/blog/2013-05-07/2-0-0/)).
  * I added the [`laxcomma` option](http://www.jshint.com/docs/options/#laxcomma) because this project uses comma-first coding style partially.