[3.6] bpo-28315: Improve code examples in docs (GH-1372) (#1445)

Replace
   File "<stdin>", line 1, in ?
with
   File "<stdin>", line 1, in <module>
(cherry picked from commit 8856940cf2e82cb17db2b684cd5732fe658605ca)
diff --git a/Doc/tutorial/classes.rst b/Doc/tutorial/classes.rst
index e134d5d..073444c 100644
--- a/Doc/tutorial/classes.rst
+++ b/Doc/tutorial/classes.rst
@@ -784,7 +784,7 @@
    'c'
    >>> next(it)
    Traceback (most recent call last):
-     File "<stdin>", line 1, in ?
+     File "<stdin>", line 1, in <module>
        next(it)
    StopIteration