Bump sphinx from 3.4.0 to 3.4.1 (#553)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.4.0 to 3.4.1.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES">sphinx's changelog</a>.</em></p>
<blockquote>
<h1>Release 3.4.1 (released Dec 25, 2020)</h1>
<h2>Bugs fixed</h2>
<ul>
<li><a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8559">#8559</a>: autodoc: AttributeError is raised when using forward-reference type
annotations</li>
<li><a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8568">#8568</a>: autodoc: TypeError is raised on checking slots attribute</li>
<li><a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8567">#8567</a>: autodoc: Instance attributes are incorrectly added to Parent class</li>
<li><a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8566">#8566</a>: autodoc: The <code>autodoc-process-docstring</code> event is emitted to the
alias classes unexpectedly</li>
<li><a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8583">#8583</a>: autodoc: Unnecessary object comparision via <code>__eq__</code> method</li>
<li><a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8565">#8565</a>: linkcheck: Fix PriorityQueue crash when link tuples are not
comparable</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/f5406b918791d9504ca6638330d89dbd86ebcb93"><code>f5406b9</code></a> Bump to 3.4.1 final</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/b94752a293c37d61ee89bc4a9f3e5b937fde525d"><code>b94752a</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8585">#8585</a> from tk0miya/8583_unnecessary_eq</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/5c39d0c0688d011a26b806f9bcc90d194ad292f0"><code>5c39d0c</code></a> Fix <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8583">#8583</a>: autodoc: Unnecessary object comparision via <code>__eq__</code> method</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/043260481b59c922fea042a1e9bbc4ff32fa1069"><code>0432604</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8581">#8581</a> from tk0miya/8566_autodoc_process_docstring_for_alia...</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/df8ab215c0c30da1de6ddadfef957b447510778a"><code>df8ab21</code></a> Fix <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8566">#8566</a>: autodoc-process-docstring is emitted to the alias classes</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/46eaa5db8005492ae2ff28208f95b9ea8dab62b5"><code>46eaa5d</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8579">#8579</a> from francoisfreitag/fix-queue</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/a1b8b1febb6ce0b7423bb78df30b0fc424c12325"><code>a1b8b1f</code></a> Ensure linkcheck items are comparable</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/955d6558ec155dffaef999d890c2cdb224cbfbb9"><code>955d655</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8571">#8571</a> from tk0miya/8567_wrong_ivars_in_parent_class</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/70bb2262d6677e5bcf2c85786b5f410a3a0f68aa"><code>70bb226</code></a> Fix <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8567">#8567</a>: autodoc: Instance attributes are incorrectly added to Parent class</li>
<li><a href="https://github.com/sphinx-doc/sphinx/commit/31cad2ebe7a205154e1374bfa52338111e515719"><code>31cad2e</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sphinx-doc/sphinx/issues/8570">#8570</a> from tk0miya/8569_getslots_TypeError</li>
<li>Additional commits viewable in <a href="https://github.com/sphinx-doc/sphinx/compare/v3.4.0...v3.4.1">compare view</a></li>
</ul>
</details>
<br />


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Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

requirements/doc.txt

@@ -1 +1 @@
-sphinx==3.4.0
+sphinx==3.4.1