upgraded maven-pmd-plugin to 3.8
diff --git a/pom.xml b/pom.xml
index 717a47f..8f52b8b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -980,7 +980,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-pmd-plugin</artifactId>
-          <version>3.7</version>
+          <version>3.8</version>
           <configuration>
             <targetJdk>${maven.compiler.target}</targetJdk>
             <rulesets>