Fixed pytest_asyncio deprecation warning.

This fixes pytest_asyncio's deprecation warning: "The 'asyncio_mode'
default value will change to 'strict' in future, please explicitly use
'asyncio_mode=strict' or 'asyncio_mode=auto' in pytest configuration
file."

Author: felixxm

setup.cfg

@@ -42,6 +42,7 @@ tests =
 
 [tool:pytest]
 testpaths = tests
+asyncio_mode = strict
 
 [flake8]
 exclude = venv/*,tox/*,specs/*