Get tests running in a headless browser on travis

[liliakai]

with mocha-phantomjs, we get failures when trying to use some modern (though not-yet official/standard) browser features, e.g.:

ReferenceError: Can't find variable: Promise

and

TypeError: '[object Uint8Array]' is not a valid argument for 'Function.prototype.apply'

[arlolra]

There's no timeline for a phantomjs 2 release.

Would you consider using Sauce Labs? It's free for open source. https://saucelabs.com/opensauce https://saucelabs.com/javascript/mocha-js

[liliakai]

:+1: Sauce Labs, with the caveat that some of our tests currently depend on the native client module, which isn't supported by selenium chrome driver.