Bump rxjava from 2.1.9 to 2.2.21

Bumps [rxjava](https://github.com/ReactiveX/RxJava) from 2.1.9 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@v2.1.9...v2.2.21)

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

Author: dependabot[bot]

pom.xml

@@ -108,7 +108,7 @@
         <javapoet.verion>1.13.0</javapoet.verion>
         <org.eclipse.jdt.version>3.10.0</org.eclipse.jdt.version>
         <org.eclipse.text.version>3.5.101</org.eclipse.text.version>
-        <rxjava.version>2.1.9</rxjava.version>
+        <rxjava.version>2.2.21</rxjava.version>
         <commons-codec.verion>1.10</commons-codec.verion>
         <jmh.version>1.29</jmh.version>
         <awscrt.version>0.12.3</awscrt.version>