Update pytest from 5.0.0 to 5.1.0 (#525)

Author: pyup-bot

requirements_dev.txt

@@ -16,7 +16,7 @@ starlette==0.12.0;python_version>="3.6"  # pyup: update minor
 coverage==4.5.1  # pyup: update minor
 flake8==3.7.1  # pyup: update minor
 tox==3.12.1  # pyup: update minor
-pytest==5.0.0  # pyup: update minor
+pytest==5.1.0  # pyup: update minor
 pytest-runner==5.1  # pyup: update minor
 pytest-asyncio==0.10.0  # pyup: update minor
 pytest-tornado5==2.0.0  # pyup: update minor