docs: fix javadoc warnings

Close #81

Author: paodb

src/main/java/com/flowingcode/vaadin/addons/orgchart/OrgChart.java

@@ -257,9 +257,9 @@ public void setNodeTemplate(String parameterName, String functionBody) {
   }
 
   /**
-   * Adds a {@link DragAndDropListener} to the component.
+   * Adds a {@link DragAndDropEvent} listener to the component.
    *
-   * @param dragAndDropListener the listener to be added.
+   * @param listener the listener to be added.
    */
   public void addDragAndDropListener(ComponentEventListener<DragAndDropEvent> listener) {
     addListener(DragAndDropEvent.class, listener);