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.
I'm going to ask that this be changed to present instead of latest, in testing building edX from scratch, this seemed to work just fine.