Scheduled weekly dependency update for week 39 (#65)

* Update pytest from 3.6.1 to 3.8.1

* Update pytest-asyncio from 0.8.0 to 0.9.0

* Update pytest-cov from 2.5.1 to 2.6.0

* Update mypy from 0.610 to 0.630

Author: pyup.io bot

requirements.txt

@@ -1,6 +1,6 @@
-pytest==3.6.1
-pytest-asyncio==0.8.0
-pytest-cov==2.5.1
+pytest==3.8.1
+pytest-asyncio==0.9.0
+pytest-cov==2.6.0
 docutils==0.14
-mypy==0.610
+mypy==0.630
 -e .