Bump pyyaml from 5.1 to 5.4

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.1 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](https://github.com/yaml/pyyaml/compare/5.1...5.4)

---
updated-dependencies:
- dependency-name: pyyaml
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -2,7 +2,7 @@ beautifulsoup4==4.11.1
 html5lib==1.1
 mwparserfromhell==0.6.4
 python-frontmatter==1.0.0
-PyYAML==5.1
+PyYAML==5.4
 six==1.16.0
 soupsieve==2.3.2.post1
 webencodings==0.5.1