fix typo in comment

compiler/types/TypeRep.lhs

@@ -322,7 +322,7 @@ funTyCon = mkFunTyCon funTyConName (mkArrowKinds [argTypeKind, openTypeKind] lif
 	-- You might think that (->) should have type (?? -> ? -> *), and you'd be right
 	-- But if we do that we get kind errors when saying
 	--	instance Control.Arrow (->)
-	-- becuase the expected kind is (*->*->*).  The trouble is that the
+	-- because the expected kind is (*->*->*).  The trouble is that the
 	-- expected/actual stuff in the unifier does not go contra-variant, whereas
 	-- the kind sub-typing does.  Sigh.  It really only matters if you use (->) in
 	-- a prefix way, thus:  (->) Int# Int#.  And this is unusual.