build(deps): bump io.reactivex.rxjava2:rxjava from 2.1.14 to 2.2.21

Bumps [io.reactivex.rxjava2:rxjava](https://github.com/ReactiveX/RxJava) from 2.1.14 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](ReactiveX/RxJava@v2.1.14...v2.2.21)

---
updated-dependencies:
- dependency-name: io.reactivex.rxjava2:rxjava
  dependency-version: 2.2.21
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -67,7 +67,7 @@ reactiveStreams = "1.0.4"
 robolectric = "4.12"            # Do not use >4.12 as it breaks the build
 runner = "1.0.2"
 rxandroid = "2.0.2"
-rxjava = "2.1.14"
+rxjava = "2.2.21"
 serialization = "1.7.3"
 slf4jNop = "2.0.17"
 spotless = "7.0.4"