eclipse-leshan#933: Correct the access level of a member variable

Signed-off-by: moznion <[email protected]>

leshan-client-core/src/main/java/org/eclipse/leshan/client/observer/LwM2mClientObserverDispatcher.java

@@ -25,7 +25,7 @@
  *
  */
 public class LwM2mClientObserverDispatcher implements LwM2mClientObserver2 {
-    protected CopyOnWriteArrayList<LwM2mClientObserver> observers = new CopyOnWriteArrayList<>();
+    private CopyOnWriteArrayList<LwM2mClientObserver> observers = new CopyOnWriteArrayList<>();
 
     public void addObserver(LwM2mClientObserver observer) {
         observers.add(observer);