make documentation sphinx 3.x compatible

docs/extensions/attributetable.py

@@ -107,7 +107,8 @@ def build_lookup_table(env):
     ignored = {
         'data', 'exception', 'module', 'class',
     }
-    for (fullname, (docname, objtype)) in domain.objects.items():
+
+    for (fullname, _, objtype, docname, _, _) in domain.get_objects():
         if objtype in ignored:
             continue