Replace DiagnosticableMixin with DiagnosticableTreeMixin

[TetsuFe]

trafficstars

To Fix #123

ref

https://github.com/dylanwuzh/flutter-cupertino-date-picker/pull/118#issuecomment-670340128

flutter doctor

$ flutter doctor Doctor summary (to see all details, run flutter doctor -v): [✓] Flutter (Channel stable, 1.20.1, on Mac OS X 10.15.6 19G73, locale ja-JP)

[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3) [✓] Xcode - develop for iOS and macOS (Xcode 11.6) [✓] Android Studio (version 3.6) [✓] VS Code (version 1.47.3) [✓] Connected device (1 available)

• No issues found!

[imshashank]

Please merge this soon.

[imshashank]

Anyone having same issue can use this->

  flutter_cupertino_date_picker:
    git:
      url: https://github.com/imshashank/flutter-cupertino-date-picker # Repo
      ref: master # Branch name

[LugonjaAleksandar]

@dylanwuzh can someone from the team who is maintaining this repo please review this? Your repo is being redirected to a fork that is going around the issue with latest Flutter. You guys need to move forward the project by supporting latest breaking changes in Flutter.

[stevenspiel]

It doesn't look like this repo is being maintained. The last commit was 5 months ago.

[elvisun]

Is anyone interested in forking this repo and submitting a new package to pub?...