Update mentions and usages of `package:lints` version to 2.0

[parlough]

Alongside Dart 2.17, the lints package will release a ^2.0.0 version with various new lints and corresponding fixes (in the SDK).

If we mention or use the old version anywhere, with the release of 2.17 we should update those references and fix any lints as necessary.

[domesticmouse]

Is flutter_lints also getting a matching major version bump?

[parlough]

@domesticmouse Yep, you can find more info here: flutter/packages#1165, but I'm not sure about the timelines on the flutter_lints side.

[goderbauer]

v2 of package:lints is published. package:flutter_lints will follow shortly as soon as flutter/packages#1165 (comment) is resolved.