add "final" to BufferingFlowableWrapper class

connectivity/service/src/main/java/org/eclipse/ditto/connectivity/service/messaging/mqtt/hivemq/client/BufferingFlowableWrapper.java

@@ -26,7 +26,7 @@
  *
  * @param <T> type of items
  */
-public class BufferingFlowableWrapper<T> implements Disposable {
+public final class BufferingFlowableWrapper<T> implements Disposable {
     private static final String DISPOSED_ERROR_MESSAGE = "The wrapper is disposed.";
 
     private final Flowable<T> originalFlowable;