Update red_black_tree.py

Author: lighting9999

data_structures/binary_tree/red_black_tree.py

@@ -1,10 +1,9 @@
 from __future__ import annotations
 
-from collections.abc import Iterator
 import doctest
+from collections.abc import Iterator
 from pprint import pformat
 
-
 class RedBlackTree:
     """
     A Red-Black tree, which is a self-balancing BST (binary search