More strictly control what goes into elm.nix

elm.nix

@@ -1,6 +1,4 @@
-{ pkgs }:
-
-with pkgs;
+{ lib, stdenv, elm, fetchElmDeps, uglify-js,  }:
 
 let
   mkDerivation =
@@ -15,10 +13,10 @@ let
     stdenv.mkDerivation {
       inherit name src;
 
-      buildInputs = [ elmPackages.elm ]
-        ++ lib.optional outputJavaScript nodePackages.uglify-js;
+      buildInputs = [ elm ]
+        ++ lib.optional outputJavaScript uglify-js;
 
-      buildPhase = pkgs.elmPackages.fetchElmDeps {
+      buildPhase = fetchElmDeps {
         elmPackages = import srcs;
         elmVersion = "0.19.1";
         inherit registryDat;