Fixed typo (#5439)

alvinphilips · web-flow · commit d32d0158a3b5 · 2021-10-19T21:39:15.000+02:00
Changed it's (it is) to its
diff --git a/data_structures/binary_tree/binary_tree_mirror.py b/data_structures/binary_tree/binary_tree_mirror.py
@@ -1,6 +1,6 @@
 """
 Problem Description:
-Given a binary tree, return it's mirror.
+Given a binary tree, return its mirror.
 """
 
 
