update sorting.py

sorting.py

 def heapSort(lista):
 
 		n = len(lista)
-		for i in range((n // 2) - 1, -1, -1):
+		n2 = (n // 2) - 1
+		nMinus = n - 1
+
+		for i in range(n2, -1, -1):
 			heapify(lista, n, i)
 
-		for i in range(n-1, -1, -1):
+		for i in range(nMinus, -1, -1):
 			lista[i], lista[0] = lista[0], lista[i]
 			heapify(lista, i, 0)