updated genericutils

src/main/java/rocks/zipcode/io/quiz4/generics/GenericUtils.java

  * @author leon on 11/12/2018.
  */
 public class GenericUtils {
-    public static <_ extends Comparable> Iterable<Iterable<_>> powerSet(Set<_> originalSet) {
+    public static <_ extends Comparable> Iterable<? extends Iterable<_>> powerSet(Set<_> originalSet) {
         return null;
     }
 
-    public static <_ extends Comparable> Iterable<Iterable<_>> powerSet(_... originalSet) {
+    public static <_ extends Comparable> Iterable<? extends Iterable<_>> powerSet(_... originalSet) {
         return powerSet(new TreeSet<>(Arrays.asList(originalSet)));
     }
 }
+