fix a bug in quicksort

Author: xtaci

include/quick_sort.h

@@ -74,8 +74,8 @@ namespace alg {
 quicksort(list, begin, pivot_idx-1);
 quicksort(list, pivot_idx+1, end);
 } else if ( begin + 1 == end) {
-if (list[begin + 1] > list[end])
-swap(list[begin + 1], list[end]);
+if (list[begin] > list[end])
+swap(list[begin], list[end]);
 }
 }
 }