Bump pyyaml from 5.1 to 5.4

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](yaml/pyyaml@5.1...5.4)

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

Author: dependabot[bot]

requirements.txt

@@ -6,7 +6,7 @@ numpy==1.16.3
 opencv-python==3.4.3.18
 pandas==0.18.1
 Pillow==8.2.0
-PyYAML==5.1
+PyYAML==5.4
 scikit-image==0.15.0
 scikit-learn==0.19.1
 scikit-surprise==1.0.4