Bump pyyaml from 3.12 to 5.4 in /contrib/mmts/tests2

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.12 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@3.12...5.4)

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

Author: dependabot[bot]

contrib/mmts/tests2/requirements.txt

@@ -8,7 +8,7 @@ dockerpty==0.4.1
 docopt==0.6.2
 jsonschema==2.6.0
 psycopg2==2.7.3.1
-PyYAML==3.12
+PyYAML==5.4
 requests==2.11.1
 six==1.11.0
 texttable==0.9.1