Changing your Travis setup to use the EU npm js mirror

Panic! all our tests on our CI systems were failing tonight. NPM's main servers were down, and that's never a good thing on a friday evening, when everyone wants to leave for the pub. 

Fortunately, the guys at #node.js on Freenode instructed everyone to use the european npm mirror. That's easy on your local machine, but what about your CI systems?

Thankfully, it's super easy to change travis' npm to point to a different mirror. On your `.travis.yml` file, add this:

- npm config set registry

Boom! sorted :)