Add the ability to request additional scopes at sign-in time.

[Ajax-ua]

Currently, when setting an additional scope, the plugin prompts the user to grant access twice: the first for sign in and the second for additional scope.
Earlier it was a restriction of the Google Sign-In iOS sdk. However sdk v6.2.0 and higher support requesting additional scopes at sign-in time. Could you please update the plugin?

[reslear]

hi @Ajax-ua it is true, @joeflateau can help with this?
google/GoogleSignIn-iOS#30