Scheduled weekly dependency update for week 17 (#274)

* Update sphinx from 1.7.3 to 1.7.4

* Update docker from 3.2.1 to 3.3.0

* Update pytest from 3.5.0 to 3.5.1

Author: pyup.io bot

requirements-dev.txt

@@ -1,13 +1,13 @@
 attrs==17.4.0
 flake8==3.5.0
-sphinx==1.7.3
+sphinx==1.7.4
 pep257==0.7.0
 -e .
 aioredis==1.1.0
 cryptography==2.2.2
-docker==3.2.1
+docker==3.3.0
 pynacl==1.2.1
-pytest==3.5.0
+pytest==3.5.1
 pytest-aiohttp==0.3.0
 pytest-cov==2.5.1
 pytest-mock==1.9.0