private void Update()
 {
     if (player != null)
     {
         if (Input.GetKey(KeyCode.D))
         {
             player.MoveRight();
         }
         if (Input.GetKey(KeyCode.A))
         {
             player.MoveLeft();
         }
         if (Input.GetKey(KeyCode.W) || Input.GetKey(KeyCode.Space))
         {
             player.Jump();
         }
     }
 }