src, nix: hlint update

This pulls in an updated hlint version from nixpkgs, and fixes some
new eta-reduction warnings. (I don't particularly think this is more
readable, but I suppose being consistently hlint-clean is worth it.)

src/PostgREST/Config.hs

@@ -175,10 +175,10 @@ class JustIfMaybe a b where
   justIfMaybe :: a -> b
 
 instance JustIfMaybe a a where
-  justIfMaybe a = a
+  justIfMaybe = identity
 
 instance JustIfMaybe a (Maybe a) where
-  justIfMaybe a = Just a
+  justIfMaybe = Just
 
 -- | Reads and parses the config and overrides its parameters from env vars,
 -- files or db settings.