title: Can't build create-react-app project with custom PUBLIC_URL
body: <p>I'm trying </p>
  
  <pre><code>PUBLIC_URL=http://example.com npm run build
  </code></pre>
  
  <p>with a project built using the latest create-react-script.</p>
  
  <p>However, the occurrences of <code>%PUBLIC_URL%</code> in <code>public/index.html</code> are replaced with an empty string, not the expected value <code>PUBLIC_URL</code>.</p>
  
  <p><code>public/index.html</code> contains code like</p>
  
  <pre><code>&lt;script src="%PUBLIC_URL%/static/js/jarvis.widget.min.js"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>Hours of searching the internet and stack overflow show that very little is written about <code>PUBLIC_URL</code>. I cloned create-react-app from GitHub and have been browsing the code but have not yet been enlightened.</p>
  
  <p>Does anyone have any suggestions as to what I'm doing wrong?</p>