update docstring for python version

Author: sayandipdutta

Lib/functools.py

@@ -236,7 +236,8 @@ def __ge__(self, other):
 
 def reduce(function, sequence, initial=_initial_missing):
     """
-    reduce(function, iterable, /, initial=None) -> value
+    reduce(function, iterable, /,
+           initial=_functools._initial_missing) -> value
 
     Apply a function of two arguments cumulatively to the items of a sequence
     or iterable, from left to right, so as to reduce the iterable to a single