Bump bleach from 3.1.1 to 3.1.2

Bumps [bleach](https://github.com/mozilla/bleach) from 3.1.1 to 3.1.2.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/mozilla/bleach/blob/master/CHANGES">bleach's changelog</a>.</em></p>
<blockquote>
<h2>Version 3.1.2 (March 11th, 2020)</h2>
<p><strong>Security fixes</strong></p>
<ul>
<li>
<p><code>bleach.clean</code> behavior parsing embedded MathML and SVG content
with RCDATA tags did not match browser behavior and could result in
a mutation XSS.</p>
<p>Calls to <code>bleach.clean</code> with <code>strip=False</code> and <code>math</code> or
<code>svg</code> tags and one or more of the RCDATA tags <code>script</code>,
<code>noscript</code>, <code>style</code>, <code>noframes</code>, <code>iframe</code>, <code>noembed</code>, or
<code>xmp</code> in the allowed tags whitelist were vulnerable to a mutation
XSS.</p>
<p>This security issue was confirmed in Bleach version v3.1.1. Earlier
versions are likely affected too.</p>
<p>Anyone using Bleach &lt;=v3.1.1 is encouraged to upgrade.</p>
<p><a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1621692">https://bugzilla.mozilla.org/show_bug.cgi?id=1621692</a></p>
</li>
</ul>
<p><strong>Backwards incompatible changes</strong></p>
<p>None</p>
<p><strong>Features</strong></p>
<p>None</p>
<p><strong>Bug fixes</strong></p>
<p>None</p>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/mozilla/bleach/commit/78a06726dd6c72a42c90c1f7a8fa5d21ebcfa587"><code>78a0672</code></a> Update for v3.1.2 release</li>
<li><a href="https://github.com/mozilla/bleach/commit/7b625ff9f6888a08037700269fb23e3ef863b8a7"><code>7b625ff</code></a> add wheel to requirements-dev</li>
<li><a href="https://github.com/mozilla/bleach/commit/e4e9e21e7aebff40c88fafa4319bba4636a602d9"><code>e4e9e21</code></a> fix bug 1621692</li>
<li>See full diff in <a href="https://github.com/mozilla/bleach/compare/v3.1.1...v3.1.2">compare view</a></li>
</ul>
</details>
<br />


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</details>

Superseded by #5407.