refac: use update/3 to change handle_topic?

Untracked files:

lib/slax_web/live/chat_room_live.ex

@@ -30,6 +30,6 @@ defmodule SlaxWeb.ChatRoomLive do
   end
 
   def handle_event("toggle-topic", _params, socket) do
-    {:noreply, assign(socket, hide_topic?: !socket.assigns.hide_topic?)}
+    {:noreply, update(socket, :hide_topic?, &(!&1))}
   end
 end