Fix eval warning: stdenv.hostPlatform.system

shell.nix

@@ -11,8 +11,8 @@ mkShell {
   inputsFrom = [ ownPkgs.default ];
   packages =
     [elixir elixir-ls]
-    ++ lib.lists.optional (pkgs.system == "x86_64-linux") inotify-tools
-    ++ lib.lists.optionals (pkgs.system == "aarch64-darwin") (with pkgs.darwin.apple_sdk.frameworks; [
+    ++ lib.lists.optional (pkgs.stdenv.hostPlatform.system == "x86_64-linux") inotify-tools
+    ++ lib.lists.optionals (pkgs.stdenv.hostPlatform.system == "aarch64-darwin") (with pkgs.darwin.apple_sdk.frameworks; [
       CoreFoundation
       CoreServices
     ]);