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.
If building from an existing installation, the error I run into is that https://github.com/edx/configuration/blob/master/playbooks/roles/xqueue/defaults/main.yml also needs to change from -npm to -nodejs

doing a quick ack, i also see npm in playbooks/roles/jenkins_admin/defaults/main.yml and playbooks/roles/jenkins_worker/defaults/main.yml