doc: fix compile error on "shoddy" example extension (GH-215)

diff --git a/Doc/includes/shoddy.c b/Doc/includes/shoddy.c
index 07a2721..0c6d412 100644
--- a/Doc/includes/shoddy.c
+++ b/Doc/includes/shoddy.c
@@ -31,7 +31,7 @@
 
 
 static PyTypeObject ShoddyType = {
-    PyObject_HEAD_INIT(NULL)
+    PyVarObject_HEAD_INIT(NULL, 0)
     "shoddy.Shoddy",         /* tp_name */
     sizeof(Shoddy),          /* tp_basicsize */
     0,                       /* tp_itemsize */