Bump pytest from 3.9.1 to 5.1.2 (#597)

Author: dependabot-preview[bot]

requirements.txt

@@ -4,7 +4,7 @@ flake8==3.5.0
 -e .[sa]
 sphinx==2.2.0
 tox==3.14.0
-pytest==3.9.1
+pytest==5.1.2
 pytest-cov==2.7.1
 pytest-sugar==0.9.2
 pytest-timeout==1.3.3