Update Mocha to v1.17.1 / Remove grunt.util.hooker

* I updated [Mocha]() to v1.17.1 and fixed expected output of the test. The console output of Mocha has been refined for the recent updates. Please see visionmedia/mocha#1006 and  visionmedia/mocha#1087 for more details.
* I updated the modules described in devDependencies. Especially, I updated `travis-cov` module from [kitcambridge/travis-cov#config](https://github.com/kitcambridge/travis-cov/tree/config) to [the original version](https://github.com/alex-seville/travis-cov), because [they are merged](https://github.com/alex-seville/travis-cov/pull/3).
* [`grunt.util.hooker`](http://gruntjs.com/api/grunt.util#grunt.util.hooker) is [deprecated](http://gruntjs.com/blog/2013-11-21-grunt-0.4.2-released). So I replaced it with [hooker](https://github.com/cowboy/javascript-hooker) module.