Update docker from 3.3.0 to 3.7.0

Author: pyup-bot

requirements-dev.txt

@@ -5,7 +5,7 @@ aiohttp==3.5.4
 aiomysql==0.0.20
 aiopg==0.16.0
 coverage==4.5.2
-docker==3.3.0
+docker==3.7.0
 flake8==3.5.0
 ipdb==0.11
 motor==1.2.2