Bump pyyaml from 5.3 to 5.4 (#189)

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3...5.4)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -9,7 +9,7 @@ idna==2.8
 jmespath==0.9.4
 nose==1.3.7
 python-dateutil==2.8.1
-PyYAML==5.3
+PyYAML==5.4
 requests==2.22.0
 s3transfer==0.3.2
 six==1.14.0