removing DerivingVia extension (not compatible ghc < 8.6.1)

Author: akhesaCaro

doc/cookbook/uverb/UVerb.lhs

@@ -12,7 +12,6 @@ handlers that respond with arbitrary open unions of types.
 {-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DerivingStrategies #-}
-{-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
@@ -158,7 +157,9 @@ Example usage:
 ```haskell
 data Foo = Foo Int Int Int
   deriving (Show, Eq, GHC.Generic, ToJSON)
-  deriving HasStatus via WithStatus 200 Foo
+
+instance HasStatus Foo where
+  type StatusOf Foo = 200
 
 data Bar = Bar
   deriving (Show, Eq, GHC.Generic, ToJSON)