Update coverage from 4.4.2 to 4.5.1

Author: pyup-bot

requirements-dev.txt

@@ -4,7 +4,7 @@ aiohttp-session==2.3.0
 aiohttp==3.0.6
 aiomysql==0.0.12
 aiopg==0.13.2
-coverage==4.4.2
+coverage==4.5.1
 docker==2.6.1
 docker-compose==1.17.1
 flake8==3.5.0