Your first game: enable CollisionShape2D again on player start (#974)

* enable collision 2d again on player start

otherwise there is no collision in a re-play

* remove monitoring line

learning/step_by_step/your_first_game.rst

@@ -323,7 +323,7 @@ the player when starting a new game.
     func start(pos):
         position = pos
         show()
-        monitoring = true
+        $CollisionShape2D.disabled = false
 
 Enemy Scene
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