Update maven-pmd-plugin from 3.5 to 3.8.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/codec/trunk@1811783 13f79535-47bb-0310-9956-ffa450edef68

Author: garydgregory

pom.xml

@@ -406,7 +406,7 @@ limitations under the License.
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-pmd-plugin</artifactId>
-        <version>3.5</version>
+        <version>3.8</version>
         <configuration>
           <targetJdk>${maven.compiler.target}</targetJdk>
           <linkXref>true</linkXref>