Revert "Remove instance for deprecated list monad transformer."

This reverts commit bc3adef.

Author: fisx

src/Data/Swagger/Declare.hs

@@ -162,6 +162,10 @@ instance MonadDeclare d m => MonadDeclare d (IdentityT m) where
   declare = lift . declare
   look = lift look
 
+instance MonadDeclare d m => MonadDeclare d (ListT m) where
+  declare = lift . declare
+  look = lift look
+
 instance MonadDeclare d m => MonadDeclare d (MaybeT m) where
   declare = lift . declare
   look = lift look