function update(req, res) {
  const { id, name, saying } = req.body;

  Hero.findOne({ id })
    .then(hero => {
      hero.name = name;
      hero.saying = saying;
      hero.save().then(() => res.json(hero))
    })
    .catch(err => {
      res.status(500).send(err);
    });
}