adjust warning

Author: L0neGamer

Control/DeepSeq.hs

@@ -533,7 +533,7 @@ instance NFData1 Fixed where liftRnf _ = rwhnf
 --  @since 1.3.0.0
 --  @deprecated 1.5.1.1
 #if __GLASGOW_HASKELL__ >= 910
-instance {-# DEPRECATED "functions cannot be in normal form" #-} NFData (a -> b) where rnf = rwhnf
+instance {-# DEPRECATED "NFData is not well-defined on function types. https://github.com/haskell/deepseq/issues/16" #-} NFData (a -> b) where rnf = rwhnf
 #else
 instance NFData (a -> b) where rnf = rwhnf
 #endif