changed null to user.id

changed null to user.id so auth can be created for new users after first user is created.

example create route taking params from registration from:

```sh
create: function(req, res, next) {
        var auth = {
                email: req.param('email'),
                password: req.param('password')
            },
            userObj = {
                name: req.param('name'),
                title: req.param('title'),
                email: req.param('email')
            };

        User.create(userObj)
            .exec(function (err, user){
                if (err){
                    sails.log.error(err);
                    req.session.flash = {
                        err: err
                    };

                    return res.redirect('/user/new');
                }
                req.session.user = user;

                user.online = true;
                req.session.authenticated = true;
                user.save(function(err, user) {
                    if(err) {
                        sails.log.error(err);
                        return next(err);
                    }

                    user.action = " signed-up and logged-in.";

                    User.publishCreate(user);
                    waterlock.engine.attachAuthToUser(auth, user, function (err) {
                        if (err) {
                            sails.log.error(err);
                            res.json(err);
                        }
                        else {
                            waterlock.logger.debug('user login success');
                            return res.redirect('/user/show/'+user.id);
                        }
                    });
                });
            });
    }
```