Specify plugin version and switch off Javadoc linting.

This eliminates Maven warnings.
Arguably we might want Javadoc linting on, but it was already switched
off using a different parameter for an older Javadoc plugin version.

pom.xml

@@ -214,8 +214,8 @@
                 <artifactId>maven-javadoc-plugin</artifactId>
                 <version>3.1.1</version>
                 <configuration>
-                    <!-- Turn off Java 8 strict Javadoc checking -->
-                    <additionalparam>-Xdoclint:none</additionalparam>
+                    <!-- Turn off strict Javadoc checking -->
+                    <doclint>none</doclint>
                 </configuration>
                 <executions>
                     <!-- Compress Javadoc into JAR and include that JAR when deploying. -->