Give him a warm water bath to clean out the wound if you haven't already and monitor. If you see swelling or he seems to be in pain, I would take him to the vet. If you do, I would make sure they do injection antibiotics as opposed to oral. Not only is oral medication ineffective for snakes due to their slow metabolism, but you don't want to be irritating the injury any more than you have to. I would also not offer food until he's healed up. He can deal with not eating for a week or two, you definitely don't want the cut to get re-opened by the strain of eating.