Upgrade maven-javadoc-plugin 3.3.1 -> 3.4.0 (#64)

See:
- https://issues.apache.org/jira/issues/?jql=project%20%3D%20MJAVADOC%20AND%20fixVersion%20%3E%203.3.1%20AND%20fixVersion%20%3C%3D%203.4.0
- apache/maven-javadoc-plugin@maven-javadoc-plugin-3.3.1...maven-javadoc-plugin-3.4.0

pom.xml

@@ -866,7 +866,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-javadoc-plugin</artifactId>
-                    <version>3.3.1</version>
+                    <version>3.4.0</version>
                     <configuration>
                         <!-- All relevant doclint checks are performed during
                         the compilation phase; no need to recheck during