Scheduled weekly dependency update for week 21 (#288)

* Update pytest from 3.5.1 to 3.6.0

* Update aiohttp from 3.2.0 to 3.2.1

* Update yarl from 1.2.3 to 1.2.4

Author: pyup.io bot

requirements-dev.txt

@@ -7,13 +7,13 @@ aioredis==1.1.0
 cryptography==2.2.2
 docker==3.3.0
 pynacl==1.2.1
-pytest==3.5.1
+pytest==3.6.0
 pytest-aiohttp==0.3.0
 pytest-cov==2.5.1
 pytest-mock==1.10.0
 pytest-sugar==0.9.1
-aiohttp==3.2.0
+aiohttp==3.2.1
 multidict==4.3.0
 chardet==3.0.4
-yarl==1.2.3
+yarl==1.2.4
 aiomcache==0.6.0