rename Client to StreamChatClient

packages/flutter_widgets/example/lib/customize_channel_preview.dart

@@ -20,7 +20,7 @@ import 'package:stream_chat_flutter/stream_chat_flutter.dart';
 ///
 /// - We retrieve the count of unread messages from [Channel.state]
 void main() async {
-  final client = Client(
+  final client = StreamChatClient(
     's2dxdhpxd94g',
     logLevel: Level.INFO,
   );
@@ -34,7 +34,7 @@ void main() async {
 }
 
 class MyApp extends StatelessWidget {
-  final Client client;
+  final StreamChatClient client;
 
   MyApp(this.client);