update changelog for 1.13 socket reference change

CHANGELOG.md

Index: CHANGELOG.md
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c88fdab70f0bff34cf7f23a46c7878d17b255955..4d3229c76044ce72d0d64be30cb7b613e00e70c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,9 +27,13 @@
     allowed by the HTTP protocol.
     The `HttpServer` still gracefully receives fragments, but discards them
     before delivering the request.
-  * Removed server socket references. The use of server socket references
-    was deprecated back in 1.9. Use the `shared` flag when creating listening
-    sockets and `HttpServer` to distribute accepted sockets between isolates.
+  * To allow connections to be accepted on the same port across different
+    isolates, set the `shared` argument to `true` when creating server socket
+    and `HttpServer` instances.
+    * The deprecated `ServerSocketReference` and `RawServerSocketReference`
+      classes have been removed.
+    * The corresponding `reference` properties on `ServerSocket` and
+      `RawServerSocket` have been removed.
 
 * `dart:isolate`
   * `Isolate` added `packageRoot` and `packageMap` getters.