updating node packages and checking for old modules on Travis

- `npm run outdated` &mdash; this will check for outdated `dependencies` and `devDependencies` and display newer version numbers in the Travis log (but not fail anything ever).
- `grunt validate-package --force` &mdash; this will check for potentially vulnerable modules in the package.json file using the nodesecurity.io database. The `--force` flag means that the exit code will always be 0 and not fail the build. If we start using shrinkwrap (see #15) then I'll switch to `grunt validate-package` instead since it is more thorough and performant.

r= @nchapman