Bump pyyaml from 5.3.1 to 5.4

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3.1 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3.1...5.4)

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

Author: dependabot[bot]

requirements.txt

@@ -29,7 +29,7 @@ pytest==5.4.1
 pytest-benchmark==3.2.3
 python-dateutil==2.8.1
 pytz==2019.3
-PyYAML==5.3.1
+PyYAML==5.4
 scikit-learn==0.22.2.post1
 scipy==1.4.1
 six==1.14.0