Add support for browserstack

[darlanmendonca]

What do you think about adding support for browserstack?

[exogen]

@darlanmendonca Sounds like a good feature! Do you know of any repos using BrowserStack in their public CI so I can experiment with the API?

[darlanmendonca]

@exogen I have this module darlanmendonca/chai-style, a to assert css from a dom element.

I set up their in Travis, and integrate with BrowserStack.
New pull requests automatically run tests in browserstack-chrome, and we can add/change others browsers

can you use this module? is my clean module (in tests), :D