Problema con NodeJS y MongoDB, usando Mongoose para la conexion.

    const express = require('express');
    const bodyParser = require('body-parser');
    const pug = require('pug');
    const db = require('mongoose');
    const app = express();
    const Schema = db.Schema;
    
    
    //vistas y configuracion
    app.set('view engine', 'pug')
    app.use(bodyParser.urlencoded({ extended: false }))
    app.use(bodyParser.json());
    app.use(express.static('public'));
 
    


    const usuarios = Schema({
        name:String,
        password:String
    })


    db.model('Usuario', usuarios)


  		//peticiones HTTP
    app.get('/', (req,res) => {
    	res.render('index');
    	console.log('Hiciste una peticion GET');
    });

    app.get('/register', (req, res) => {
        res.render('register')
    })


	app.post('/', (req,res) => {
		console.log('POST /api/product')
        console.log(req.body)

        let user = new Usuario()
        user.email = req.body.email
        user.password = req.body.password

        user.save((err,saved) =>{
            if(err) res.status(500).send({message: "Error al salver "})
            res.status(200).send({user: saved})
            })
	   });


    db.createConnection('mongodb://localhost:27017/project', (err, res) =>{
        app.listen(80, 'localhost', () => {
            console.log("Servidor iniciado correctamente en:  puerto 80");
        })

        if (err) {
            console.log("Error al conectar a la base de datos");
        }else{
           console.log("Base de datos conectada") 
        }
    });

extends ./layouts.pug
block contenido
	body
		div(class="container")
			form(action='/', method="POST", class="form-signin")
				.container
					form.form-signin
					h2.form-signin-heading Please Login
					label.sr-only(for='inputEmail') Email address
					input#inputEmail.form-control(type='email', placeholder='Email address', ref="email", name="email" required, autofocus='')
					label.sr-only(for='inputPassword') Password
					input#inputPassword.form-control(type='password', ref="password", placeholder='Password', required, name="password")
					.checkbox
					label
					input(type='checkbox', value='remember-me')
					|  Remember me
					a.btn.btn-sm.btn-secondary.btn-block(href="/register") Sign Up
					button.btn.btn-lg.btn-primary.btn-block(type='submit') Log in