title: Trying to list collection of Firestore Database
body: <p>I'd like to list of the collection of Firestore database inside Ionic4 app so I use the <a href="https://googleapis.dev/nodejs/firestore/latest/Firestore.html#listCollections" rel="noreferrer">doc</a> in the section listCollection so I applied the example code in my code : </p>
  
  <pre><code>this.afs.firestore.listCollections().then(collections =&gt; {
    for (let collection of collections) {
      console.log(`Found collection with id: ${collection.id}`);
    }
  });
  </code></pre>
  
  <p>here is my constructor : </p>
  
  <pre><code>  constructor(private router: Router,
                private afs: AngularFirestore,
                private fireauth: AngularFireAuth) { }
  </code></pre>
  
  <p>And I get this error : error TS2339: Property 'listCollections' does not exist on type 'Firestore'.</p>
  
  <p>I can not use the property listCollections whereas it is in the online doc... </p>