Add use strict to heap sort

Author: mgechev

src/sorting/heapsort/heapsort.js

@@ -1,5 +1,7 @@
 (function (exports) {
 
+  'use strict';
+
   function comparator(a, b) {
     return a - b;
   }
@@ -16,18 +18,21 @@
      *
      * @private
      * @param {array} array Array
-     * @param {number} index Index of the element which palce in the max heap should be found.
+     * @param {number} index Index of the element which palce in
+     *                       the max heap should be found.
      */
     function heapify(array, index, heapSize, cmp) {
       var left = 2 * index + 1,
           right = 2 * index + 2,
           largest = index;
 
-      if (left < heapSize && cmp(array[left], array[index]) > 0)
+      if (left < heapSize && cmp(array[left], array[index]) > 0) {
         largest = left;
+      }
 
-      if (right < heapSize && cmp(array[right], array[largest]) > 0)
+      if (right < heapSize && cmp(array[right], array[largest]) > 0) {
         largest = right;
+      }
 
       if (largest !== index) {
         var temp = array[index];