JS dependencies will not install correctly

http://docs.coala.io/en/latest/Users/Install.html#js-dependencies states that you run `npm install -g` to install JS dependencies, however that only installs the coala-bears globally (which is useless) not each of the dependencies stated in [package.json](https://github.com/coala/coala-bears/blob/master/package.json) (e.g. eslint) globally.

When running `npm install -g` what's actually happening is:
- npm installs all dependencies stated in `package.json` locally (node_modules folder inside the project)
- npm creates a symlink to coala-bears folder inside their 'global dependencies folder' (try `npm root -g` to find where it actually is)