title: CORS error when using jsonPlaceHolder and react-admin
body: <p>I am receiving a CORS error when trying to get data from <a href="https://jsonplaceholder.typicode.com" rel="nofollow noreferrer">https://jsonplaceholder.typicode.com</a>.</p>
  
  <p>I have tested this on Google Chrome, Brave Browser, Firefox and Safari. 
  I am following with the tutorial on the website. My code is as follows:</p>
  
  <pre><code>import React from 'react';
  import { Admin, Resource, ListGuesser } from 'react-admin';
  import jsonServerProvider from 'ra-data-json-server';
  import './App.css';
  
  const dataProvider = jsonServerProvider('https://jsonplaceholder.typicode.com');
  const App = () =&gt; (
    &lt;Admin dataProvider={dataProvider}&gt;
      &lt;Resource name='users' list={ListGuesser} /&gt;
    &lt;/Admin&gt;
  );
  
  export default App;
  
  </code></pre>
  
  <p>Error: </p>
  
  <pre><code>Access to fetch at 'https://jsonplaceholder.typicode.com/users?_end=10&amp;_order=ASC&amp;_sort=id&amp;_start=0' from origin 'http://192.168.1.175:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
  </code></pre>
  
  <p>I have tried using:</p>
  
  <pre><code>/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --disable-web-security
  </code></pre>
  
  <p>to open Chrome and I still receive the error</p>