Node.js tutoria: Use await when calling run()

As it happens, the run() call is the last call in the app, so it also works without
await. But the moment somebody
adds code after run(), they'd be surprised
that it gets called
"before" run. So await for good measure.

docs/tutorial/node/src/main_tiles_from_js.js

@@ -18,6 +18,6 @@ for (let i = tiles.length - 1; i > 0; i--) {
 let model = new slint.ArrayModel(tiles);
 mainWindow.memory_tiles = model;
 
-mainWindow.run();
+await mainWindow.run();
 
 // ANCHOR_END: main