Add Read typeclass to Stage

src/Network/Wai/Serve/Types.hs

@@ -74,7 +74,7 @@ instance FromJSON MiddlewareStack where
 -- also listens for TLS connections and has additional middlewares that only
 -- make sense on a public server.
 --
-data Stage = Development | Staging | Production deriving (Show, Generic)
+data Stage = Development | Staging | Production deriving (Show, Generic, Read)
 
 instance FromJSON Stage where
   parseJSON = genericParseJSON defaultOptions