unbreak functor/monad issue in old ghc vers

src/Monad.hs

@@ -49,7 +49,7 @@ import Control.Monad
 #endif
 
 concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b]
-concatMapM f xs = fmap concat (mapM f xs)
+concatMapM f xs = liftM concat (mapM f xs)
 
 liftM' :: Monad m => (a -> b) -> m a -> m b
 liftM' = (<$!>)