code: function update(req, res, next) {
    var body = req.body;
    delete body.username;
  
    db.users.update(req.params.user, body, function(err, user) {
      if(err) { return next(err); }
      res.json(201, user);
    });
  }
docs: URL: /users/:user
  
  Method: PUT
  
  Status codes:
  
  * `201` if the user was updated successfully