Updated heap.py

heap.py

 
 		# If necessary, this changes root by swapping va-
 		# lues
-		lista[i], lista[largest] = lista[largest], lista[i]
+        if largest != i:
+            lista[i], lista[largest] = lista[largest], lista[i]
 
 		# This heapifies the root repeatedly
 		heapify(lista, n, largest)