Update pytest-mock from 1.10.0 to 1.11.2 (#578)

Author: pyup-bot

requirements_dev.txt

@@ -20,7 +20,7 @@ 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
-pytest-mock==1.10.0  # pyup: update minor
+pytest-mock==1.11.2  # pyup: update minor
 pytest-cov==2.7.1  # pyup: update minor
 
 # docs