title: Firestore get() all documents in a collection returns an error
body: <p>I'm trying to iterate all the documents in the collection with the get() method as defined in the <a href="https://firebase.google.com/docs/firestore/query-data/get-data#get_all_documents_in_a_collection" rel="nofollow noreferrer">documentation</a>, however it doesn't work for me. I get a <code>get is not a function</code> error, what am I doing wrong? </p>
  
  <pre><code>export class MainComponent implements OnInit {
      selectedCharacter: number = null;
      people: Observable&lt;any&gt;;
      private peopleCollection: AngularFirestoreCollection&lt;Character&gt;;
  
      constructor(private db: AngularFirestore,
            private route: ActivatedRoute,
            private location: Location) {
        this.peopleCollection = db.collection('people');
        this.people = this.peopleCollection.valueChanges();
  
        this.route.params.subscribe(
            params =&gt; (this.selectedCharacter = +params['id'])
        );
      }
  
      ngOnInit() {
          this.peopleCollection.get().then(function(querySnapshot) {
              querySnapshot.forEach(function(doc) {
                  console.log(doc.id, " =&gt; ", doc.data());
              });
          });
     }
  }
  </code></pre>