AndroidX migration requires change of major version

Official [documentation](https://flutter.dev/docs/development/packages-and-plugins/androidx-compatibility#for-plugin-maintainers-migrating-a-flutter-plugin-to-androidx) suggests following:
> Make sure to increment the major version of your plugin for this change and clearly document it in your plugin’s changelog. This breaking change requires manual migration for users to fix. Pub treats digits differently depending on whether a plugin is pre- or post-1.0.0. The very first digit is the major version for plugins that are at or above 1.0.0. For plugins below 1.0.0, the middle digit is considered to the major version.

It was a breaking change for us, because of usage another plugin that uses old support library.
So just letting you know, that some users might have same problems as well, because of unexpected migration to AndroidX.