Update Maven PMD and FindBugs plugins.

Author: garydgregory

pom.xml

@@ -254,15 +254,15 @@ CSV files of various types.
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-pmd-plugin</artifactId>
-        <version>3.6</version>
+        <version>3.8</version>
         <configuration>
           <targetJdk>${maven.compiler.target}</targetJdk>
         </configuration>
       </plugin>
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>findbugs-maven-plugin</artifactId>
-        <version>3.0.3</version>
+        <version>3.0.4</version>
       </plugin>
       <plugin>
         <groupId>org.codehaus.mojo</groupId>