Updated .travis.yml to build with node versions 0.6, 0.8 and 0.10

Travis no longer has Node 0.4 available (see http://docs.travis-ci.com/user/languages/javascript-with-nodejs/ for the available versions), and so all builds are failing. This removes 0.4 from the list of Node versions to build against, and adds the latest stable version 0.10.