finished lambda expression

src/main/java/com/zipcoder/payment/PaymentPresenter.java

 
     public String toStringById(Payment[] p){
         Arrays.sort(p,
-                (Payment a, Payment b) -> {  return Integer.signum((int)(a.getId() - b.getId())); }
-        );
+                (Payment a, Payment b) ->  Long.compare(b.getId(),a.getId()));
         StringBuilder answer = new StringBuilder();
 
         for(Payment payment: p){