Bump maven-pmd-plugin from 3.9.0 to 3.20.0

Bumps [maven-pmd-plugin](https://github.com/apache/maven-pmd-plugin) from 3.9.0 to 3.20.0.
- [Release notes](https://github.com/apache/maven-pmd-plugin/releases)
- [Commits](https://github.com/apache/maven-pmd-plugin/compare/maven-pmd-plugin-3.9.0...maven-pmd-plugin-3.20.0)

---
updated-dependencies:
- dependency-name: org.apache.maven.plugins:maven-pmd-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index 776bb6e..2f11f8f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -235,7 +235,7 @@
       <!-- Requires setting 'export MAVEN_OPTS="-Xmx512m -XX:MaxPermSize=128m" ' -->

       <plugin>

         <artifactId>maven-pmd-plugin</artifactId>

-        <version>3.9.0</version>

+        <version>3.20.0</version>

         <configuration>

           <targetJdk>${maven.compiler.target}</targetJdk>

         </configuration>