renamed [pytest] to [tools:pytest] in config, due to recommendation

setup.cfg

@@ -54,7 +54,7 @@ packages =
 # py.test options when running `python setup.py test`
 #addopts = tests
 
-[pytest]
+[tool:pytest]
 # Options for py.test:
 # Specify command line options as you would do when invoking py.test directly.
 # e.g. --cov-report html (or xml) for html/xml output or --junitxml junit.xml