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 considered this and actually thought it might be a preferable way to go about adding the ppa.  I only decided to add it to the edxapp role, because that's where I saw npm getting added via apt.  Thus I thought it might be easier to follow for the reviewers and any potential future users who were just diving into the project.