fixing checkAuth()

app.js

function checkAuth(req, res, next) {
  if (req.headers.authtoken) {
    admin.auth().verifyIdToken(req.headers.authtoken)
      .then(() => {
        next()
      }).catch(() => {
        res.status(403).send('Unauthorized')
      });
  } else {
    res.status(403).send('Unauthorized')
  }
}