Update pytest from 4.1.0 to 4.2.0 (#431)

Author: pyup-bot

requirements_dev.txt

@@ -15,7 +15,7 @@ quart==0.8.0;python_version>="3.7"  # pyup: update minor
 coverage==4.5.1  # pyup: update minor
 flake8==3.7.1  # pyup: update minor
 tox==3.7.0  # pyup: update minor
-pytest==4.1.0  # pyup: update minor
+pytest==4.2.0  # pyup: update minor
 pytest-runner==4.2  # pyup: update minor
 pytest-asyncio==0.10.0  # pyup: update minor
 pytest-tornado5==2.0.0  # pyup: update minor