Update Nix packaging to reference wai-cors dep

nix/PaymentServer.nix

@@ -64,6 +64,7 @@ in { system, compiler, flags, pkgs, hsPkgs, pkgconfPkgs, ... }:
           (hsPkgs."servant-server" or (buildDepError "servant-server"))
           (hsPkgs."wai" or (buildDepError "wai"))
           (hsPkgs."wai-extra" or (buildDepError "wai-extra"))
+          (hsPkgs."wai-cors" or (buildDepError "wai-cors"))
           (hsPkgs."data-default" or (buildDepError "data-default"))
           (hsPkgs."warp" or (buildDepError "warp"))
           (hsPkgs."warp-tls" or (buildDepError "warp-tls"))