added ansible task to add chris-lea ppas for current version nodejs

I added a task to use chris-lea's repos for nodejs.  In other parts of the program, it seems like these repos are preferred to the default ubuntu repos ([see this](https://github.com/edx/edx-platform/blob/master/requirements/system/ubuntu/apt-repos.txt)).  This will keep the nodejs version current as well.

Separately, I fixed a typo where "npm" was listed twice.  Although "nodejs" does not need to be explicitly listed because it is a dependency of npm, I added it for people that may not be familiar with npm.
You may want to change this to `edxapp_chrislea_ppa: "ppa:chris-lea/node.js"`, it should not be an array.

(And everywhere else)