Update pyyaml from 5.1 to 5.1.1

Author: pyup-bot

dev-requirements.txt

@@ -18,7 +18,7 @@ pylint==2.3.1  # Lint
 pyroma==2.5  # Packaging best practices checker
 pytest-cov==2.7.1  # Measure code coverage
 pytest==4.6.0  # Test runners
-PyYAML==5.1
+PyYAML==5.1.1
 Sphinx==2.1.0
 sphinx-autodoc-typehints==1.6.0
 sphinxcontrib-spelling==4.2.1