Proposing different approach to sum numbers

- Updated MediumNumbersProblemSolution.java

There is a boxing cost while doing arithmetic operations on Wrapper types. Although it wouldn't make much difference for this learning exercise but just wanted to propose this small change as many new developers will read this guide.

Author: The-Wardaddy

src/test/java/com/github/streams/practice/b_medium/numbers/MediumNumbersProblemSolution.java

@@ -38,7 +38,7 @@ public static <T> List<T> getUniqueNumberFromList(List<T> input) {
   }
 
   public static long sumOfNumbers(List<Integer> input) {
-    return input.stream().reduce(0, Integer::sum);
+    return input.stream().mapToInt(Integer::intValue).sum();
   }
 
   public static long sumOfUniqueNumbers(List<Integer> input) {