Bump pyyaml from 5.3 to 5.3.1

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3 to 5.3.1.
- [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...5.3.1)

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

requirements.txt

@@ -18,7 +18,7 @@ pypiwin32==219; sys_platform == 'win32' and python_version < '3.6'
 pypiwin32==223; sys_platform == 'win32' and python_version >= '3.6'
 PySocks==1.7.1
 python-dotenv==0.13.0
-PyYAML==5.3
+PyYAML==5.3.1
 requests==2.22.0
 texttable==1.6.2
 urllib3==1.25.9; python_version == '3.3'