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](https://github.com/yaml/pyyaml/compare/5.3.1...5.4)

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

requirements.txt

@@ -65,7 +65,7 @@ PySocks==1.7.1
 python-dateutil==2.8.1
 pytz==2019.3
 PyWavelets==1.1.1
-PyYAML==5.3.1
+PyYAML==5.4
 pyzmq==19.0.0
 requests==2.23.0
 scikit-image==0.16.2