adding min example with method reference and Optional

Author: raoulDoc

src/main/java/lambdasinaction/chap4/Reducing.java

@@ -17,5 +17,8 @@ public static void main(String...args){
 
         int max = numbers.stream().reduce(0, (a, b) -> Integer.max(a, b));
         System.out.println(max);
+        
+        Optional<Integer> min = numbers.stream().reduce(Integer::min);
+        min.ifPresent(v -> System.out.println(v));
     }
 }