Removed reference to issue #4 from TODO items

Removed reference to issue #4 from TODO items, since issue #4 is now resolved with [4fa7005](https://github.com/bbyars/mountebank/commit/4fa70051ef308879c687aaed686aad71ac77b55d).
Merge pull request #11 from moodmosaic/patch-1

Removed reference to issue #4 from TODO items