fix issue #4 not disposing the client when disposing StreamChat widget

example/lib/main.dart

@@ -28,11 +28,9 @@ class MyApp extends StatelessWidget {
           brightness: Brightness.light,
         ),
       ),
-      home: Container(
-        child: StreamChat(
-          client: client,
-          child: ChannelListPage(),
-        ),
+      home: StreamChat(
+        client: client,
+        child: ChannelListPage(),
       ),
     );
   }

lib/src/stream_chat.dart

@@ -240,7 +240,6 @@ class StreamChatState extends State<StreamChat> {
 
   @override
   void dispose() {
-    widget.client.dispose();
     _subscriptions.forEach((s) => s.cancel());
     _queryChannelsLoadingController.close();
     _channelsController.close();