old_contents: 'use strict';
  
  const express = require('express');
  const app     = express();
  
  app.use(express.static('.'));
  
  const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;
  
  const server = app.listen(DEFAULT_PORT, () => {
      const host = server.address().address;
      const port = server.address().port;
  
      console.info('App listening at https://${host}:${port}');
  });
  
new_contents: 'use strict';
  
  const express = require('express');
  const app     = express();
  
  app.use(express.static('.'));
  
  const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;
  
  const server = app.listen(DEFAULT_PORT, () => {
      const host = server.address().address;
      const port = server.address().port;
  
      console.info('App listening at https://' + host + ':' + port);
  });
  
subject: Fix syntax error