Fix README / Update Mocha and Chai

* I updated the URL in README from [UglifyJS v1.x](https://github.com/mishoo/UglifyJS) to [v2.x](https://github.com/mishoo/UglifyJS2). This plugin uses the latter.
* I updated the year of copyright from 2013 to 2014.
* I updated all devDependencies.