Adding Firebase dependencies

This final part should be completed in the app, regardless of the system you are using. Perform the following steps to add the Firebase dependencies: 

• Add the following dependencies to pubspec.yaml (please check the latest versions at https://firebase.flutter.dev/):

firebase_core: ^1.1.0
firebase_auth: ^1.1.2
cloud_firestore: ^1.0.7

You now have completed the configuration of both an iOS and an Android app to use the Firebase platform.