update single_conversation example

lib/src/channel_image.dart

@@ -0,0 +1,25 @@
+import 'package:cached_network_image/cached_network_image.dart';
+import 'package:flutter/material.dart';
+import 'package:stream_chat/stream_chat.dart';
+
+class ChannelImage extends StatelessWidget {
+  const ChannelImage({
+    Key key,
+    @required this.channel,
+  }) : super(key: key);
+
+  final Channel channel;
+
+  @override
+  Widget build(BuildContext context) {
+    return CircleAvatar(
+      radius: 20,
+      backgroundImage: channel.extraData.containsKey('image')
+          ? CachedNetworkImageProvider(channel.extraData['image'] as String)
+          : null,
+      child: channel.extraData.containsKey('image')
+          ? null
+          : Text(channel.config.name[0]),
+    );
+  }
+}