Bump pyyaml from 5.1.1 to 5.4

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.1.1 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/5.1.1...5.4)

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

requirements.txt

@@ -11,7 +11,7 @@ pip>=9.0.1
 pygments==2.1.3
 pylint==1.9.3
 pyOpenSSL==19.0.0
-pyyaml==5.1.1
+pyyaml==5.4
 requests==2.22.0
 setuptools==30.4.0
 six==1.10.0