Update coverage from 4.4.1 to 4.4.2 (#299)

Author: pyup.io bot

requirements-dev.txt

@@ -4,7 +4,7 @@ aiohttp-session==1.0.1
 aiohttp==2.2.5
 aiomysql==0.0.9
 aiopg==0.13.1
-coverage==4.4.1
+coverage==4.4.2
 docker-compose==1.16.1
 docker-py==1.10.6
 flake8==3.4.1