Remove usage of internal api

app/multiplayer/MultiplayerExtension.js

@@ -36,7 +36,7 @@ export default class MultiplayerExtension extends Extension {
     // only once we have authenticated successfully do we initalize awareness.
     // we could send this earlier, but getting authenticated faster is more important
     provider.on("authenticated", () => {
-      provider.awareness.setLocalStateField("user", user);
+      provider.setAwarenessField("user", user);
     });
 
     // only once an actual change has been made do we add the userId <> clientId