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] <support@dependabot.com>

requirements.txt

@@ -1,4 +1,4 @@
-PyYaml==5.3
+PyYaml==5.3.1
 azure-common==1.1.24
 azure-mgmt-dns==3.0.0
 boto3==1.12.11