NextJS config doesn't work

next.config.js

const sass = require('@zeit/next-sass');
const getRoutes = require('./routes');

module.exports = sass();
module.exports = {
    exportPathMap: getRoutes
}

routes.js

module.exports = () => {
    return {
        '/': { page: '/' },
        '/404': { page: '/404' },
        '/about': { page: '/about' },
        '/p': {page: '/post'}
    }
}

server.js

const express = require('express');
const next = require('next');
const { parse } = require('url');

const dev = process.env.NODE_ENV !== 'production';
const PORT = process.env.PORT || 3000;

const app = next({dir: '.', dev });
const handle = app.getRequestHandler();

const getRoutes = require('./routes');

const routes = getRoutes();
app.prepare().then(() => {
  const server = express();
  server.get('*', (req, res) => {
    const parsedUrl = parse(req.url, true);
    const { pathname, query = {} } = parsedUrl;
    const route = routes[pathname];
    if (route) {
      return app.render(req, res, route.page, query);
    }
    return handle(req, res);
  });

  server.listen(PORT, err => {
    if (err) throw err;
    console.log(`> Ready on http://localhost:${PORT}`);
  });
});