Test cleanup.

- **[important]** Allow `npm test` to run `mocha` even if `mocha` isn't installed globally.
- **[minor]** If you don't pass anything to a `mocha` `it()`, then it treats the function as synchronous and you don't need to call `done()`.
- **[silly]** Use `mocha`'s `spec` output cuz it's pretty. And useful. I like how it displays errors more, too.
- **[silly]** Set `NODE_ENV` to `test` when testing and make it so `wiredep` doesn't have extra output when that is so.