Node.js 0.4 and 0.6 are ancient; things don't work there.
Update Travis CI configuration accordingly.
Note, that the npm update in Travis is needed for 0.8 only at the moment.
Per 0262b4244c - if you're going to stop testing on 0.8, you should be testing on 0.12.
Also allow failures on unstable nodes and "older than two latest" `io.js` versions, and enable "sudo: false" which makes tests run faster.
