Fixed bad platform repositioning
Fixed bad platform repositioning

This was due to an arithmetic mistake.

Fixes #117

walls-of-doom/walls-of-doom,mafagafogigante/walls-of-doom,walls-of-doom/walls-of-doom,walls-of-doom/walls-of-doom,walls-of-doom/walls-of-doom,mafagafogigante/walls-of-doom,mafagafogigante/walls-of-doom