socket is now sequential and not concurrent

src/main/java/ch/usi/inf/sa4/sanmarinoes/smarthut/socket/SensorSocketEndpoint.java

@@ -58,9 +58,9 @@ public class SensorSocketEndpoint extends Endpoint {
      * @return number of successful transfer
      */
     public long broadcast(Object message, User u) {
-        final Collection<Session> sessions = authorizedClients.get(u);
+        final HashSet<Session> sessions = new HashSet<>(authorizedClients.get(u));
+
         return sessions.stream()
-                .parallel()
                 .filter(
                         s -> {
                             if (s.isOpen()) return true;