testris: fixed the diff logic
testris: fixed the diff logic

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