Update pytest to 3.3.1 (#174)

* Update pytest from 3.3.0 to 3.3.1

* Update pytest from 3.3.0 to 3.3.1

requirements/py27-tests.txt

@@ -1,6 +1,6 @@
 mock==2.0.0
 mozlog==3.5
-pytest==3.3.0
+pytest==3.3.1
 pytest-metadata==1.5.1
 pytest-selenium==1.11.3
 pytest-xdist==1.20.1

requirements/py36-tests.txt

@@ -1,5 +1,5 @@
 mock==2.0.0
-pytest==3.3.0
+pytest==3.3.1
 pytest-metadata==1.5.1
 pytest-selenium==1.11.3
 pytest-xdist==1.20.1