Added missing CallDeferred() to C# Example (#2358)

* Added missing `CallDeferred()` to C# Example

The note below the example references the call_deferred from the GDScript example but it was missing in the C# one.

* Apply suggestions from code review

getting_started/step_by_step/your_first_game.rst

@@ -467,7 +467,7 @@ Add this code to the function:
     {
         Hide(); // Player disappears after being hit.
         EmitSignal("Hit");
-        GetNode<CollisionShape2D>("CollisionShape2D").Disabled = true;
+        GetNode<CollisionShape2D>("CollisionShape2D").SetDeferred("disabled", true);
     }
 
 Each time an enemy hits the player, the signal is going to be emitted. We need