fix minor typo
fix minor typo

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