Fix a typo, discovered by Joonas Paalasmaa.

Backported to 2.3
diff --git a/Doc/dist/dist.tex b/Doc/dist/dist.tex
index 87fc984..17db70b 100644
--- a/Doc/dist/dist.tex
+++ b/Doc/dist/dist.tex
@@ -555,8 +555,8 @@
 
 \begin{verbatim}
 Extension(...,
-          define_macros=[('NDEBUG', '1')],
-                         ('HAVE_STRFTIME', None),
+          define_macros=[('NDEBUG', '1'),
+                         ('HAVE_STRFTIME', None)],
           undef_macros=['HAVE_FOO', 'HAVE_BAR'])
 \end{verbatim}