Update mocha from 0.14 to 1.22.

With mocha 0.14.x, we're getting warnings during `npm update`:

```
npm WARN engine mocha@0.14.1: wanted: {"node":">= 0.4.x < 0.8.0"} (current: {"node":"v0.10.29","npm":"1.4.18"})
```

mocha is now on 1.22.x, so we're pretty far out-of-date.