Now add the cola, Shaoxing wine, dark soy sauce, light soy sauce, and (if using), the orange peel and cinnamon stick. Bring it to a boil, cover the lid, and turn down the heat to medium. Let simmer for 12-15 minutes--until the sauce is almost dry (though there should still be a small pool of sauce at the bottom of the wok). Stir the wings, and add salt to taste.