maven-javadoc-plugin is not marked as @threadsafe, which leads to a warning shown during parallel builds

[java] [WARNING] *****************************************************************
[java] [WARNING] * Your build is requesting parallel execution, but project *
[java] [WARNING] * contains the following plugin(s) that are not marked as *
[java] [WARNING] * @threadSafe to support parallel building. *
[java] [WARNING] * While this /may/ work fine, please look for plugin updates *
[java] [WARNING] * and/or request plugins be made thread-safe. *
[java] [WARNING] * If reporting an issue, report it against the plugin in *
[java] [WARNING] * question, not against maven-core *
[java] [WARNING] *****************************************************************
[java] [WARNING] The following plugins are not marked @threadSafe in ab-plugin:
[java] [WARNING] org.apache.maven.plugins:maven-javadoc-plugin:2.8.1
[java] [WARNING] *****************************************************************