Update pytest from 3.5.1 to 3.6.0

requirements.txt

 psutil==5.4.4
 py==1.5.3
 pyglet==1.3.2
-pytest==3.5.1
+pytest==3.6.0
 python-dateutil==2.7.3
 PyYAML==3.12
 redis==2.10.6