FIx incorrect Node label in "Your first game"

In the HUD section, one of the new nodes created is named "Message". The OnMessageTimerTimeout() description in the docs incorrectly refers to this as "MesageLabel". This would cause a runtime error and also does not match the actual code repository linked in the docs.

getting_started/step_by_step/your_first_game.rst

@@ -1145,7 +1145,7 @@ functions:
 
     public void OnMessageTimerTimeout()
     {
-        GetNode<Label>("MessageLabel").Hide();
+        GetNode<Label>("Message").Hide();
     }
 
 Connecting HUD to Main