chore(travis): simplify and improve config
chore(travis): simplify and improve config

Includes the following changes:
- Run tests on macOS and Windows as well.
- Run tests against the current Node.js LTS version (v10.x).
- Cache npm cache directory between builds.

gkalpak/angular-seed,bvd/componium,bvd/componium,angular/angular-seed,gkalpak/angular-seed,angular/angular-seed