Bump pytest-mock from 3.5.1 to 3.6.1 (#884)

Author: dependabot[bot]

requirements/requirements_dev.txt

@@ -16,5 +16,5 @@ pytest-black==0.3.12
 pytest-cov==2.12.1
 pytest-datadir==1.3.1
 pytest-flake8==1.0.7
-pytest-mock==3.5.1
+pytest-mock==3.6.1
 pytest-pylint==0.18.0