Install Node.js on Mac laptops

I think most of us have Node.js on our machines. Some common reasons to
install it include:

* Installing CoffeeScript, Bower, and other JavaScript packages.
* Developing on Ralph, our Hubot instance, which runs Express.js.
Use NVM to manage Node versions
Merge branch 'refs/heads/dc-mac-node' into master
Removed unneeded setup