Update js-yaml and devDependencies / Fix the links in banner

* I updated [js-yaml](https://github.com/nodeca/js-yaml), [mocha](hub.com/visionmedia/mocha), [should](https://github.com/visionmedia/should.js/) and [istanbul](https://github.com/gotwarlost/istanbul).
  * js-yaml v2.1.x uses `require.extensions` to load YAML files via `require()`, which is [the *deprecated* part of Node](http://nodejs.org/api/globals.html#globals_require_extensions). From [js-yaml v3.1.0](https://github.com/nodeca/js-yaml/blob/master/HISTORY.md#310--2014-07-07), this feature is removed.
* I updated the links in the banner comment of lib/svgo.js.