Fix typo in "adventures"

[TheMaster3558]

In adventure.py, when there is no mob in a hard mode adventure, the message sent has a typo. The word "adventures" was changed to "adventurers".

[aikaterna]

Fixed in https://github.com/aikaterna/gobcog/commit/5f9d131f5d9ff30a8a214055c5304753191666b8