title: FirebaseUser show error and Receiving error when create & sign in with email and password
body: <p>I receive an error in flutter when creating a user sign in method using FirebaseAuth and FirebaseUser. Mainly telling me to either cast or change FirebaseUser to AuthResult both of which leads to a failure to create a firebase user resulting in No implementation found for method createUserWithEmailAndPassword on channel plugins.flutter.io/firebase_auth.</p>
  <p>I have tried the responses from Android Studio without luck. The best fix is to revert to an earlier FirebaseAuth version. I'm currently using version: firebase_auth: 0.18.0+1.</p>
  <p>when I write this line of code  FirebaseUser user = await FirebaseAuth.instance.signInWithEmailAndPassword(email: _email, password: _password);
  itshow an error and 'FirebaseUser' is deprecated and shouldn't be used. Class Firestore is deprecated, use 'FirebaseFirestore' instead..
  Try replacing the use of the deprecated member with the replacement.dartdeprecated_member_use
  And same withfirestore
  sdk dependencies
  firebase_core: 0.5.0
  cloud_functions: 0.6.0
  firebase_storage: 4.0.0
  firebase_auth: 0.18.0+1</p>