Upgraded dokka-maven-plugin from 1.8.10 to 1.8.20 (#284)

Bumps [dokka-maven-plugin](https://github.com/Kotlin/dokka) from 1.8.10 to 1.8.20.
- [Release notes](https://github.com/Kotlin/dokka/releases)
- [Commits](Kotlin/dokka@v1.8.10...v1.8.20)

---
updated-dependencies:
- dependency-name: org.jetbrains.dokka:dokka-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: John Freeman <john.freeman.opensource@gmail.com>

pom.xml

@@ -132,7 +132,7 @@
         <plugin>
           <groupId>org.jetbrains.dokka</groupId>
           <artifactId>dokka-maven-plugin</artifactId>
-          <version>1.8.10</version>
+          <version>1.8.20</version>
         </plugin>
       </plugins>
     </pluginManagement>