Special member is not documented with automodule

[kasium]

Describe the bug
If I have a module which has a special attribute (starting with a double underscore) it will not be documented by automodule even if it's specified in :special-members:. According to my research it's because it's not identified as an attribute.

If a non-special attribute is used, everything works fine.

To Reproduce

module.py

#: mydoc
__dummy__ = 2
#: mydoc
dummy = 2

doc.rst

.. automodule:: my_project
   :members:
   :undoc-members:
   :show-inheritance:
   :private-members:
   :special-members: __dummy__

To execute the build I use python setup.py build_sphinx

Expected behavior
The attribute should be documented.

Environment info

• OS: Linux
• Python version: 3.7.1
• Sphinx version: 3.5.4