Upgrade javadoc plugin (#570)

Author: nilknow

pom.xml

@@ -241,7 +241,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-javadoc-plugin</artifactId>
-                <version>3.2.0</version>
+                <version>3.4.0</version>
                 <executions>
                     <execution>
                         <id>attach-javadocs</id>