title: react-admin fetch header X-Total-Count issue
body: <p>When use <code>react-admin</code> from frontend to call backend API, got this error from browser console:</p>
  
  <pre><code>Warning: Missing translation for key: "The X-Total-Count header is missing in the HTTP Response. The jsonServer Data Provider expects responses for lists of resources to contain this header with the total number of results to build the pagination. If you are using CORS, did you declare X-Total-Count in the Access-Control-Expose-Headers header?"
  </code></pre>
  
  <p>If use <code>ng-admin</code> to call the backend API, it works well.</p>