Tests: Change mocha reporter `spec` -> `dot`

We've already discussed reporters here: #90 
I chose `dot` over `nyan` because the latter visually breaks with multi-line `console.log` outputs:

![screen shot 2013-11-13 at 18 11 15](https://f.cloud.github.com/assets/872004/1531897/bea10d7a-4c6e-11e3-9bc1-6ced672888a0.png)
![screen shot 2013-11-13 at 18 11 28](https://f.cloud.github.com/assets/872004/1531898/bf364052-4c6e-11e3-9dcb-64e798f67bf7.png)