Update maven-pmd-plugin from 3.8 to 3.12.0.

Author: Gary Gregory

pom.xml

@@ -349,7 +349,7 @@ limitations under the License.
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-pmd-plugin</artifactId>
-        <version>3.8</version>
+        <version>3.12.0</version>
         <configuration>
           <targetJdk>${maven.compiler.target}</targetJdk>
           <linkXref>true</linkXref>