nix: Add a tool for checking Haskell imports and exports (#1768)

src/PostgREST/Config.hs

@@ -16,6 +16,7 @@ Other hardcoded options such as the minimum version number also belong here.
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE LambdaCase            #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE QuasiQuotes           #-}
 {-# LANGUAGE ScopedTypeVariables   #-}
 {-# LANGUAGE TemplateHaskell       #-}
 {-# OPTIONS_GHC -fno-warn-type-defaults #-}