Add DeriveAnyClass to UVerb.lhs (not implied by DerivingVia on 8.6.5)

Author: Gaël Deest

doc/cookbook/uverb/UVerb.lhs

@@ -15,6 +15,7 @@ handlers that respond with arbitrary open unions of types.
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}