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] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -2,7 +2,7 @@ future==0.18.2
 iso8601==0.1.12
 pyserial==3.4
 python-periphery==2.0.1
-PyYAML==5.3.1
+PyYAML==5.4
 flake8==3.8.3
 pytest==5.4.3
 pytest-cov==2.8.1