Set up SauceLabs for browser testing

We ran into an issue where Funcunit was throwing an error on Chrome 58 on Windows 10: https://github.com/canjs/canjs/issues/3235. We should set up SauceLabs testing for funcunit so we can catch these issues earlier.

Setting up SauceLabs is relatively easy using the [test-saucelabs](https://github.com/bitovi/test-saucelabs) package like we are using in canjs here: https://github.com/canjs/canjs/blob/master/test/test-sauce-labs.js.