wrong github repository declared

[rivasdiaz]

Hello

I was reading about this package in https://pub.dev/packages/flutter_gtk and noticed that the links to the repo points to a different repo (expands_widget). It wasn't hard to find the real one, but I noticed you have the wrong homepage in your pubspec.yaml

This package looks very promising. Thanks for your work.

[jesusrp98]

See #4