Fix wrong listener in README.md (dart-lang/web_socket_channel#18)

pkgs/web_socket_channel/README.md

diff --git a/pkgs/web_socket_channel/README.md b/pkgs/web_socket_channel/README.md
index 2ea4408..c1abd7a 100644
--- a/pkgs/web_socket_channel/README.md
+++ b/pkgs/web_socket_channel/README.md
@@ -91,7 +91,7 @@
 main() async {
   var channel = new IOWebSocketChannel.connect("ws://localhost:8181");
   channel.sink.add("connected!");
-  channel.sink.listen((message) {
+  channel.stream.listen((message) {
     // ...
   });
 }
@@ -120,7 +120,7 @@
 main() async {
   var channel = new HtmlWebSocketChannel.connect("ws://localhost:8181");
   channel.sink.add("connected!");
-  channel.sink.listen((message) {
+  channel.stream.listen((message) {
     // ...
   });
 }