Update brace-expansion.py

Author: kamyu104

Python/brace-expansion.py

@@ -12,7 +12,7 @@ def expand(self, S):  # nested is fine
         :rtype: List[str]
         """
         def form_words(options):
-            words = list(map("".join, itertools.product(*options)))
+            words = map("".join, itertools.product(*options))
             words.sort()
             return words