title: how to use react-firebase-hooks in firebase web v9
body: <p>I am using 'react-firebase-hooks',  firebase web v9. I have this error : &quot; TypeError: <em>firebase__WEBPACK_IMPORTED_MODULE_2</em>_.db.collection is not a function&quot;</p>
  <p>This is the code causing the issue:</p>
  <pre class="lang-js prettyprint-override"><code>import { useCollection } from 'react-firebase-hooks/firestore';
  
  const [realtimePosts, loading, error] = useCollection(
    db.collection('posts').orderBy('timestamp', 'desc')
  );
  </code></pre>