adding a couple of npm scripts and tweaking travis

Added 2 new tasks:
1. `npm run outdated` &mdash; Looks for outdated npm modules in package.json. Informational only and won't fail any Travis builds. This also uses `--depth 0` so it only checks top-level modules, not pointless sub-sub-sub dependencies.
2. `npm run audit-shrinkwrap` &mdash; Uses [**nsp**](https://github.com/nodesecurity/nsp) to check a npm-shrinkwrap.json file for any known vuln modules in the https://nodesecurity.io database. This script will create a npm-shrinkwrap.json file and uses `|| true` to make sure the exit code is always 0 so it won't fail the Travis build.

**NOTE:** I'm installing **nsp** in the .travis.yml file, so if you want to run this locally, we'd need to:
a) install the **nsp** module globally using `npm i nsp -g`, or
b) install the **nsp** module locally as a devDep.

Because npm scripts don't need the `./node_modules/.bin/` junk, I think the package.json and .travis.yml wouldn't need to be altered either way.

I also tweaked the .travis.yml file to log out any known questionable modules using `npm run audit-shrinkwrap`.