Update TypePredicate.java

Update TypePredicate.java to use isClient method.

This changes is made to maintain consistency.

src/main/java/seedu/address/model/person/TypePredicate.java

@@ -20,9 +20,9 @@ public TypePredicate(String type) {
     @Override
     public boolean test(Person person) {
         if (type.equals("housekeeper")) {
-            return person instanceof Housekeeper;
+            return !person.isClient();
         } else if (type.equals("client")) {
-            return person instanceof Client;
+            return person.isClient();
         } else {
             return false;
         }