ensureInitialized() missing before setPreferredOrientations()

[maganap]

@flutter 1.12.13+hotfix.5
From: https://codelabs.developers.google.com/codelabs/flutter-cupertino/#2

On the first run of this lab, an error shows up when calling setPreferredOrientations() in main() because WidgetsFlutterBinding.ensureInitialized(); needs to be called first.

That line of code is missing from the codelab. Adding it solves the issue.

[stevenyix]

this fixed the issue for me, too.

the codelab code sample here should be updated, too:
https://codelabs.developers.google.com/codelabs/flutter-cupertino/#2