port for heroku

server.js

@@ -1,10 +1,11 @@
 const express = require('express');
 const app = express();
+const PORT = process.env.PORT || 3000;
 
 app.get('/', (req, res)=>{
     res.send('this works');
 })
 
-app.listen(3000, ()=>{
+app.listen(PORT, ()=>{
     console.log('listening...');
 })