chore(publish): prepare for v2.0.0

Author: hoc081098

example/lib/main.dart

@@ -9,7 +9,7 @@ import 'package:rxdart_ext/state_stream.dart';
 void main() => runApp(const MyApp());
 
 class MyApp extends StatelessWidget {
-  const MyApp({Key? key}) : super(key: key);
+  const MyApp({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -22,7 +22,7 @@ class MyApp extends StatelessWidget {
 }
 
 class MyHomePage extends StatelessWidget {
-  const MyHomePage({Key? key}) : super(key: key);
+  const MyHomePage({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -47,7 +47,7 @@ class MyHomePage extends StatelessWidget {
 }
 
 class MainPage extends StatefulWidget {
-  const MainPage({Key? key}) : super(key: key);
+  const MainPage({super.key});
 
   @override
   State<MainPage> createState() => _MainPageState();