Update integration test example.
They changed the URL to the TODO MVC.
Changed to newer version of Mocha & Chai for unit testing.
Turns out Testem comes bundled with a stupidly old version of Chai. Switching to a custom version fixed some issues:
* Chai as promised now works.
* Sinon-Chai now works as expected.

I also switched from using a custom-built version of Sinon to an officially built version.