update dependencies

This is just an dependency update to omit the npm deprecated warnings triggered by node-minify.
```
npm WARN deprecated uglify-js2@2.1.11: You can now install this using uglify-js@2.2.0 node_modules/uglify-js
npm WARN deprecated ├── source-map@0.1.8 (amdefine@0.0.4)
npm WARN deprecated └── optimist@0.3.5 (wordwrap@0.0.2)
```