Bump pyyaml from 5.1 to 5.4 in /requirements
Bump pyyaml from 5.1 to 5.4 in /requirements

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)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
mozilla/bedrock,alexgibson/bedrock,craigcook/bedrock,pascalchevrel/bedrock,mozilla/bedrock,alexgibson/bedrock,flodolo/bedrock,mozilla/bedrock,pascalchevrel/bedrock,MichaelKohler/bedrock,flodolo/bedrock,MichaelKohler/bedrock,alexgibson/bedrock,pascalchevrel/bedrock,mozilla/bedrock,craigcook/bedrock,craigcook/bedrock,craigcook/bedrock,flodolo/bedrock,sylvestre/bedrock,flodolo/bedrock,pascalchevrel/bedrock,sylvestre/bedrock,sylvestre/bedrock,MichaelKohler/bedrock,sylvestre/bedrock,MichaelKohler/bedrock,alexgibson/bedrock