Bump pyyaml from 5.3 to 5.3.1

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3 to 5.3.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3...5.3.1)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements_dev.txt

@@ -7,5 +7,5 @@ tox==3.14.3
 coverage==5.0.3
 Sphinx==2.3.1
 cryptography==3.2
-PyYAML==5.3
+PyYAML==5.3.1