hydra: l0dables.nix args

hydra/l0dables.nix

+{ rustManifest ? ./channel-rust-nightly.toml,
+  mozillaOverlay ? import <mozillaOverlay>,
+  pkgs ? (import <nixpkgs> { overlays = [ mozillaOverlay ]; }),
+}:
 let
-  rustManifest = ./channel-rust-nightly.toml;
-  mozillaOverlay = import <mozillaOverlay>;
-  pkgs = (import <nixpkgs> { overlays = [ mozillaOverlay ]; });
   pkgs' = pkgs // {
     rustChannelOfTargets = _channel: _date: targets:
       (pkgs.lib.rustLib.fromManifestFile rustManifest {