Bump pyyaml from 3.11 to 5.1

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.11 to 5.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](https://github.com/yaml/pyyaml/compare/3.11...5.1)

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

requirements.txt

@@ -1 +1 @@
-PyYAML==3.11
+PyYAML==5.1

setup.py

@@ -14,7 +14,7 @@ setup(
     packages=find_packages(),
     license="MIT",
     install_requires=[
-        "PyYAML==3.11",
+        "PyYAML==5.1",
     ],
     classifiers=[
         "Intended Audience :: Developers",