chore(package.json): remove `post-install` script

This will instead be done manually by the user, or in a `before_script`
by travis.
chore(test): add support for unit tests on Sauce

CHANGES
- new gulp task `cloudtest` – opens a tunnel to the Sauce server and
runs unit tests on Safari
- change `npm test` to run `cloudtest` instead of `test` (this will
help with CI integration)
chore(travis): add .travis.yml