2d platformer gun cooldown fix (#686)

Restart cooldown timer when gun has fired

2d/platformer/src/Actors/Gun.gd

@@ -22,4 +22,5 @@ func shoot(direction = 1):
 	bullet.set_as_toplevel(true)
 	add_child(bullet)
 	sound_shoot.play()
+	timer.start()
 	return true