Update pytest from 3.3.2 to 3.4.2 (#447)

Author: pyup.io bot

requirements.txt

@@ -6,7 +6,7 @@ flake8==3.4.1
 -e .[sa]
 sphinx==1.7.1
 tox==2.8.1
-pytest==3.3.2
+pytest==3.4.2
 pytest-cov==2.5.1
 pytest-sugar==0.9.0
 pytest-timeout==1.2.1