Set fixed screen orientation to 'portrait up'

lib/main.dart

@@ -63,6 +63,8 @@ class _MainState extends State<Main> {
 
   @override
   Widget build(BuildContext context) {
+    SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);
+
     return MaterialApp(
       debugShowCheckedModeBanner: false,