message: don't use now.alias when determining the assetPrefix
diff: const next = require('next')
  const {createServer} = require('http')
  const {parse} = require('url')
  -const nowConfig = require('./now.json')
  const port = parseInt(process.env.PORT, 10) || 3000
  const app = next({dev: process.env.NODE_ENV !== 'production'})
  const handle = app.getRequestHandler()
  -const deployURL = process.env.NOW_URL || nowConfig.alias
  -const deployHost = deployURL ? parse(deployURL).host : undefined
  +const deployURL = process.env.NOW_URL
  +const deployHost = deployURL && parse(deployURL).host
  app.prepare().then(() => {
  createServer((req, res) => {
  