Updating the example to match the new API (flutter#1155)

Author: davidair

packages/firebase_auth/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.8.0+2
+
+* Update Google sign-in example in the README.
+
 ## 0.8.0+1
 
 * Update a broken dependency.

packages/firebase_auth/README.md

@@ -61,12 +61,15 @@ final FirebaseAuth _auth = FirebaseAuth.instance;
 You can now use the Firebase `_auth` to authenticate in your Dart code, e.g.
 ```dart
 Future<FirebaseUser> _handleSignIn() async {
-  GoogleSignInAccount googleUser = await _googleSignIn.signIn();
-  GoogleSignInAuthentication googleAuth = await googleUser.authentication;
-  FirebaseUser user = await _auth.signInWithGoogle(
+  final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
+  final GoogleSignInAuthentication googleAuth = await googleUser.authentication;
+
+  final AuthCredential credential = GoogleAuthProvider.getCredential(
     accessToken: googleAuth.accessToken,
     idToken: googleAuth.idToken,
   );
+  
+  final FirebaseUser user = await _auth.signInWithCredential(credential);
   print("signed in " + user.displayName);
   return user;
 }

packages/firebase_auth/pubspec.yaml

@@ -4,7 +4,7 @@ description: Flutter plugin for Firebase Auth, enabling Android and iOS
   like Google, Facebook and Twitter.
 author: Flutter Team <[email protected]>
 homepage: https://github.com/flutter/plugins/tree/master/packages/firebase_auth
-version: "0.8.0+1"
+version: "0.8.0+2"
 
 flutter:
   plugin: