Bump pyyaml from 5.1.1 to 5.1.2

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.1.1 to 5.1.2.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](https://github.com/yaml/pyyaml/commits)

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

requirements.txt

@@ -6,7 +6,7 @@ coverage==4.5.4
 idna==2.8
 ply==3.11
 pyhcl==0.3.12
-PyYAML==5.1.1
+PyYAML==5.1.2
 requests==2.22.0
 six==1.12.0
 toml==0.10.0