Update sphinx to 3.4.1

[pyup-bot]

This PR updates Sphinx from 3.4.0 to 3.4.1.

Changelog

3.4.1

=====================================

Bugs fixed
----------

* 8559: autodoc: AttributeError is raised when using forward-reference type
annotations
* 8568: autodoc: TypeError is raised on checking slots attribute
* 8567: autodoc: Instance attributes are incorrectly added to Parent class
* 8566: autodoc: The ``autodoc-process-docstring`` event is emitted to the
alias classes unexpectedly
* 8583: autodoc: Unnecessary object comparision via ``__eq__`` method
* 8565: linkcheck: Fix PriorityQueue crash when link tuples are not
comparable

Links

• PyPI: https://pypi.org/project/sphinx
• Changelog: https://pyup.io/changelogs/sphinx/
• Homepage: http://sphinx-doc.org/