title: Concurrently run Express and Create-React-App issue
body: <p>I've built a simple base application using Express and Create-React-App (<a href="http://myfirst-reactapp.herokuapp.com/" rel="nofollow noreferrer">http://myfirst-reactapp.herokuapp.com/</a>). My project is split into two parts: one is the server (it has a package.json and an index.js file) and the other one is the client (which was created using npm create-react-app).<br><br>
  I am trying to redirect the users from the server side to the client side (For example localhost:5000/test will redirect to localhost:3000/test), but after deploying it to <strong>Heroku</strong>, I got the following error, and could not find an answer that solves the issue:<br><br></p>
  
  <blockquote>
    <p><strong>Uncaught SyntaxError: Unexpected token &lt;</strong></p>
  </blockquote>
  
  <h3>index.js</h3>
  
  <pre><code>const express = require('express');
  const app = express();
  const path = require('path');
  
  if (process.env.NODE_ENV === 'production') {
      app.use(express.static('/client/build'));
  
      app.get('*', (req, res) =&gt; {
          res.sendFile(path.resolve(__dirname, 'client', 'build', 'index.html'));
      });
  }
  
  const PORT = process.env.PORT || 5000;
  app.listen(PORT);
  </code></pre>
  
  <h3>package.json (server)</h3>
  
  <pre><code>{
    "name": "heroku_base",
    "version": "1.0.0",
    "description": "",
    "main": "index.js",
    "engines": {
      "node": "6.11.2",
      "npm": "3.10.10"
    },
    "scripts": {
      "start": "node index.js",
      "heroku-postbuild": "NPM_CONFIG_PRODUCTION=false npm install --prefix client &amp;&amp; npm run build --prefix client"
    },
    "keywords": [],
    "author": "",
    "license": "ISC",
    "dependencies": {
      "express": "^4.16.2"
    }
  }
  </code></pre>