Support null safety

[IchordeDionysos]

This is a request to add support for null safety to package:holding_gesture.
We depend on your awesome package, so would be great to have null safety enabled.

The Dart/Flutter team already encourages publishing the migrated packages: See this blog post.

See the migration guide for details about enabling null safety.

[gildaswise]

Thanks for using it! It's up now! https://pub.dev/packages/holding_gesture/versions/1.0.0-dev

[IchordeDionysos]

@gildaswise wow thanks for your quick response 😍 Really appreciate it 💪