0.3.1 Small Fix

What's changed from 0.3.0?

• Fix to a certain false virus detection from 0.3.0, really, your PC should be okay when you open the last version even if there is a virus "detected" in it, because it was a false positive 'caused by a certain flaw of GameMaker that is used within my system that makes the system in the installer acts like virus. Hopefully, it has no more false positive now.
• Fix to difficulty change (with bookshelf) with old savedata (of 0.2.0)