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](https://github.com/yaml/pyyaml/compare/5.1...5.4)

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

requirements.txt

@@ -5,7 +5,7 @@ vdf>=3.3
 gevent>=1.3.0
 protobuf>=3.0.0
 gevent-eventemitter~=2.1
-PyYAML==5.1
+PyYAML==5.4
 cachetools>=3.0.0
 enum34==1.1.2; python_version < '3.4'
 win-inet-pton; python_version == '2.7' and sys_platform == 'win32'