use the Documenter.objpath attribute

since this is also what import_object uses (see https://github.com/sphinx-doc/sphinx/blob/master/sphinx/ext/autodoc/importer.py)

Author: Chilipp

autodocsumm/__init__.py

@@ -618,7 +618,7 @@ def get_items_from_documenters(self, documenters):
             real_name = documenter.fullname
             display_name = documenter.object_name
             if display_name is None:  # for instance attributes
-                display_name = real_name.split('.')[-1]
+                display_name = documenter.objpath[-1]
             if check_module and not documenter.check_module():
                 continue