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

@@ -13,7 +13,7 @@ pyaes==1.6.1
 pycryptodome==3.9.8
 pyDes==2.0.1
 pytz==2019.3
-PyYAML==5.3.1
+PyYAML==5.4
 requests==2.23.0
 six==1.15.0
 soupsieve==2.0.1