Add zuul support

I found [zuul tool](https://github.com/defunctzombie/zuul) which easily solves #49 issue.
However, I have must fixed our tests a little to make them passed in a sauce cloud.

Now browser support badge looks
[![Sauce Test Status](https://saucelabs.com/browser-matrix/baby-loris.svg)](https://saucelabs.com/u/baby-loris)

Our tests don't work in IE. Probably, we should use `expect` instead of `should`. Or maybe it doesn't handle returning a promise from a test.

I need your opinions.