flutter firebase MissingPluginException

I just added firebase to my flutter App, i followed all the steps correctly, but i'm getting an error when initializing the app

this is my code to initialize app

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: new ThemeData(
        canvasColor: Colors.white,
      ),
      home: PersistentTabsDemo(),
      onGenerateRoute: route.controller,
    );
  }
}

this are the dependecies i added to pubsec.yaml

  firebase_core: ^1.6.0
  firebase_analytics: ^8.3.1
  firebase_auth: ^3.1.0
  cloud_firestore: ^2.5.1

and this is the error

Error: MissingPluginException(No implementation found for method Firebase#initializeCore on channel
plugins.flutter.io/firebase_core)

Edit: i tried removing async and await from my main class now i'm getting new error

No firebase App 'default' has been created - call Firebase.intializeApp()