HashSetvBitSetTest: use diamond operator (closes #264)

Use Java 7's diamond operator to make the code a tad more elegant, as
done in the rest of the codebase.

src/test/java/org/apache/commons/lang3/HashSetvBitSetTest.java

@@ -39,7 +39,7 @@ public class HashSetvBitSetTest {
 
     @Benchmark
     public int[] testHashSet() {
-        final HashSet<Integer> toRemove = new HashSet<Integer>();
+        final HashSet<Integer> toRemove = new HashSet<>();
         int found = 0;
         for (int i = 0; i < numberOfElementsToCompute; i++) {
             toRemove.add(found++);