Update pytest from 3.2.5 to 3.3.0

requirements.txt

 py==1.5.2
 pyglet==1.3.0
 pyparsing==2.2.0
-pytest==3.2.5
+pytest==3.3.0
 pytest-cov==2.5.1
 pytest-timeout==1.2.0
 pytest-xdist==1.20.1