Bump maven-pmd-plugin from 3.20.0 to 3.21.0 (#511)

Author: dependabot[bot]

pom.xml

@@ -53,7 +53,7 @@
     <nexus.plugin.version>1.6.13</nexus.plugin.version>
     <owasp.plugin.version>8.2.1</owasp.plugin.version>
     <projectinfo.plugin.version>3.4.4</projectinfo.plugin.version>
-    <pmd.plugin.version>3.20.0</pmd.plugin.version>
+    <pmd.plugin.version>3.21.0</pmd.plugin.version>
     <site.plugin.version>3.12.1</site.plugin.version>
     <release.plugin.version>3.0.0</release.plugin.version>
     <resources.plugin.version>3.3.1</resources.plugin.version>