Update Cloud Firestore Usage.mx (#6221)
Update Cloud Firestore Usage.mx (#6221)

The withConverter example needed to specify the type in angle brackets because toJson() can not be called on Object class. This is also how the code is written on the pub.dev example page.
firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire