Update pytest from 3.3.0 to 3.3.1

requirements.txt

 psutil==5.4.2
 py==1.5.2
 pyglet==1.3.0
-pytest==3.3.0
+pytest==3.3.1
 python-dateutil==2.6.1
 PyYAML==3.12
 redis==2.10.6