Bump gradle-versions-plugin from 0.20.0 to 0.21.0 (#30)
Bump gradle-versions-plugin from 0.20.0 to 0.21.0 (#30)

Bumps [gradle-versions-plugin](https://github.com/ben-manes/gradle-versions-plugin) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/ben-manes/gradle-versions-plugin/releases)
- [Commits](https://github.com/ben-manes/gradle-versions-plugin/compare/v0.20.0...v0.21.0)
gabrielittner/auto-value-extension-util