Bump pyyaml from 5.3.1 to 5.4 in /examples/research_projects/lxmert
Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3.1 to 5.4.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/yaml/pyyaml/blob/master/CHANGES">pyyaml's changelog</a>.</em></p>
<blockquote>
<p>5.4 (2021-01-19)</p>
<ul>
<li><a href="https://github-redirect.dependabot.com/yaml/pyyaml/pull/407">yaml/pyyaml#407</a> -- Build modernization, remove distutils, fix metadata, build wheels, CI to GHA</li>
<li><a href="https://github-redirect.dependabot.com/yaml/pyyaml/pull/472">yaml/pyyaml#472</a> -- Fix for CVE-2020-14343, moves arbitrary python tags to UnsafeLoader</li>
<li><a href="https://github-redirect.dependabot.com/yaml/pyyaml/pull/441">yaml/pyyaml#441</a> -- Fix memory leak in implicit resolver setup</li>
<li><a href="https://github-redirect.dependabot.com/yaml/pyyaml/pull/392">yaml/pyyaml#392</a> -- Fix py2 copy support for timezone objects</li>
<li><a href="https://github-redirect.dependabot.com/yaml/pyyaml/pull/378">yaml/pyyaml#378</a> -- Fix compatibility with Jython</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/yaml/pyyaml/commit/58d0cb7ee09954c67fabfbd714c5673b03e7a9e1"><code>58d0cb7</code></a> 5.4 release</li>
<li><a href="https://github.com/yaml/pyyaml/commit/a60f7a19c0b418fe95fcf2ec0957005ae39e1090"><code>a60f7a1</code></a> Fix compatibility with Jython</li>
<li><a href="https://github.com/yaml/pyyaml/commit/ee98abd7d7bd2ca9c7b98aa19164fd0306a3f3d2"><code>ee98abd</code></a> Run CI on PR base branch changes</li>
<li><a href="https://github.com/yaml/pyyaml/commit/ddf20330be1fae8813b8ce1789c48f244746d252"><code>ddf2033</code></a> constructor.timezone: _<em>copy</em> &amp; <strong>deepcopy</strong></li>
<li><a href="https://github.com/yaml/pyyaml/commit/fc914d52c43f499224f7fb4c2d4c47623adc5b33"><code>fc914d5</code></a> Avoid repeatedly appending to yaml_implicit_resolvers</li>
<li><a href="https://github.com/yaml/pyyaml/commit/a001f2782501ad2d24986959f0239a354675f9dc"><code>a001f27</code></a> Fix for CVE-2020-14343</li>
<li><a href="https://github.com/yaml/pyyaml/commit/fe150624146ee631bb0f95e45731e8b01281fed6"><code>fe15062</code></a> Add 3.9 to appveyor file for completeness sake</li>
<li><a href="https://github.com/yaml/pyyaml/commit/1e1c7fb7c09e9149967c208a6fd07276a6140d57"><code>1e1c7fb</code></a> Add a newline character to end of pyproject.toml</li>
<li><a href="https://github.com/yaml/pyyaml/commit/0b6b7d61719fbe0a11f0980489f1bf8ce746c164"><code>0b6b7d6</code></a> Start sentences and phrases for capital letters</li>
<li><a href="https://github.com/yaml/pyyaml/commit/c97691596eec279ef9191a9b3bba583a17139d5a"><code>c976915</code></a> Shell code improvements</li>
<li>Additional commits viewable in <a href="https://github.com/yaml/pyyaml/compare/5.3.1...5.4">compare view</a></li>
</ul>
</details>
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</details>
Looks like pyyaml is up-to-date now, so this is no longer needed.