changing quickSort() so it can be overridden

Sorting/QuickSorter.java

@@ -14,7 +14,7 @@ public class QuickSorter extends Sorter{
         quickSort(0,numbers.length-1);
     }
 
-    private void quickSort(int lowIndex, int highIndex){
+    void quickSort(int lowIndex, int highIndex){
        if(compare(lowIndex,highIndex)<0){
             int pivot = partition(lowIndex, highIndex);
             quickSort(lowIndex, pivot-1);