Use packages

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

lib/default.nix

@@ -1,5 +1,8 @@
 { pkgs, ... }:
+let
+  callPackage = pkgs.lib.callPackageWith { inherit pkgs; };
+in
 {
-  fetchers = import ./fetchers { inherit pkgs; };
-  runtime = import ./runtime { inherit pkgs; };
+  fetchers = callPackage ./fetchers { };
+  runtime = callPackage ./runtime { };
 }