fixed collecition containing flags

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

src/main/java/de/srsoftware/widerhall/data/ListMember.java

@@ -391,7 +391,7 @@ public class ListMember {
      * @return
      */
     public String stateText() {
-        var words = new ArrayList<String>();
+        var words = new TreeSet<String>();
         if (isAwaiting()) words.add(t("awaiting confirmation"));
         if (isModerator()) words.add(t("moderator"));
         if (isOwner()) words.add(t("owner"));