Bump rxjava from 2.2.20 to 2.2.21 (#3920)
Bump rxjava from 2.2.20 to 2.2.21 (#3920)

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 2.2.20 to 2.2.21.
- [Release notes](https://github.com/ReactiveX/RxJava/releases)
- [Changelog](https://github.com/ReactiveX/RxJava/blob/v2.2.21/CHANGES.md)
- [Commits](https://github.com/ReactiveX/RxJava/compare/v2.2.20...v2.2.21)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>

Co-authored-by: dependabot-preview[bot] <6a4c1c4838f800d1998274cd5234e1f65c55e90c@users.noreply.github.com>
douggie/XChange