Fixing issues #79 and #80.

- closes #79 [Latest grunt-mocha module requires grunt update.](https://github.com/coreyti/showdown/issues/79)
- closes #80 [Grunt lint task needs to be updated with Grunt upgrade.](https://github.com/coreyti/showdown/issues/80)

```
> grunt test

Running "simplemocha:all" (simplemocha) task
path.existsSync is now called `fs.existsSync`.

  .........................................................

  ✔ 57 tests complete (44ms)


Running "jshint:src" (jshint) task
>> 5 files lint free.

Running "jshint:test" (jshint) task
>> 1 file lint free.
```