Add java 11 support for #987 (o-t) (#1051)

* Use java 11

* Use .of
- Replace Arrays.asList with List.of
- Replace HashSet<>(List.of()) with Set.of

* Formatting

servant/src/main/java/com/iluwatar/servant/App.java

@@ -26,7 +26,6 @@ package com.iluwatar.servant;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.util.ArrayList;
 import java.util.List;
 
 
@@ -60,9 +59,7 @@ public class App {
     King k = new King();
     Queen q = new Queen();
 
-    List<Royalty> guests = new ArrayList<>();
-    guests.add(k);
-    guests.add(q);
+    List<Royalty> guests = List.of(k, q);
 
     // feed
     servant.feed(k);