extract.py: updated for python3 compatability
extract.py: updated for python3 compatability

LearnProgramming/learntris,geugon/learntris,WhitmanH/learntris,nbgraham/learntris,BigRoss/learntris,DTSCode/learntris-haskell,Shamash2014/spice_and_html,Shamash2014/spice_and_html,TylerLau/learntris,Shamash2014/spice_and_html,bschaef14/learntris,bschaef14/learntris,mosegontar/learntris,BigRoss/learntris,lochanaeg/learntris,tangentstorm/learntris,Larsharaldjoh/Tetris,bschaef14/learntris,TylerLau/learntris,SultansDream/testris