Mocha wrapper appears to be broken

# Crap

It looks like the Mocha wrapper is broken.
## Justification:
1. Take [your example code](https://github.com/glenjamin/checkers#usage-with-mocha)
2. Change the property to assert that `3 > 5`, meaning it should break every time
3. Watch it report pass
## Observation:

It smelled funky to me that there was an `it/2` in the example code, and also an `it/2` inside the wrapper. I've used Mocha for almost three hours now, and my understanding is that `it`s do not nest.

Therefore, I removed the interior `it/2` from the wrapper. Suddenly things started working.

I also `return`ed the value of the `forAll`, pretty much just because.
## Suggested remediation:
1. Observe that my garbage fixes it
2. Figure out why
3. Throw my gargbage out, because the author (me) didn't put in any effort
4. Fix it correctly instead
5. Accept that nobody ever does this, ever
6. Merge the PR