Update heap_sort.py

Author: yyeltsyn

sorts/heap_sort.py

@@ -7,7 +7,7 @@
 python3 -m doctest -v heap_sort.py
 
 For manual testing run:
-python insertion_sort.py
+python heap_sort.py
 '''
 
 from __future__ import print_function
@@ -46,7 +46,7 @@ def heap_sort(unsorted):
     n = len(unsorted)
     for i in range(n//2 - 1, -1, -1):
         heapify(unsorted, i, n)
-    for i in range(n - 1, -1, -1):
+    for i in range(n - 1, 0, -1):
         unsorted[0], unsorted[i] = unsorted[i], unsorted[0]
         heapify(unsorted, 0, i)
     return unsorted