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.
Also, I suppose that something could be done with https://github.com/edx/configuration/blob/master/playbooks/roles/common/defaults/main.yml#L87.

Something like

    - name: add apt extra repositories
      apt_repository: >-
        repo={{ item }}
      with_items: common_apt_extra_repositories

With

    common_apt_extra_repositories:
      - 'ppa:git-core/ppa'
      - 'ppa:chris-lea/node.js'