Support for build_runner v2

[Diaga]

Thank you for building this amazing idea, I have watched your tutorial video and read the docs, and I believe the Flutter community could benefit a lot from this.

Unfortunately, I have been unable to integrate framy with my project with the following error:

Running "flutter pub get" in project...                           

Because framy_generator >=0.2.2 depends on yaml ^2.2.1 and build_runner >=2.0.0 depends on yaml ^3.0.0, framy_generator >=0.2.2 is incompatible with build_runner >=2.0.0.
So, because chief depends on both build_runner ^2.0.6 and framy_generator ^0.3.3, version solving failed.
pub get failed (1; So, because chief depends on both build_runner ^2.0.6 and framy_generator ^0.3.3, version solving failed.)
Process finished with exit code 1

I believe this is linked to #160