Update nested calls-in-order test (#17).

The version in 55fea45e89d2b37032b81af39b0cff1f9e19deb6 had two problems:
- There was a bug in Sinon.JS, cjohansen/Sinon.JS#248, that made it so that the test would pass even if the last spy was never called. This defeated the entire purpose of the test.
- Even with that fixed, it was intolerant toward implementations that don't fire off all handlers at once, but instead have internal queues that are recursively flushed. So, a delay was added before checking the call order.
Pin Mocha to a later version.
Version 1.2.1