Use pytest instead of py.test per upstream recommendation, #dropthedot (#4236)

http://blog.pytest.org/2016/whats-new-in-pytest-30/
https://twitter.com/hashtag/dropthedot
diff --git a/docs/development/getting-started.rst b/docs/development/getting-started.rst
index 96b4b6d..953ae95 100644
--- a/docs/development/getting-started.rst
+++ b/docs/development/getting-started.rst
@@ -61,7 +61,7 @@
 
 .. code-block:: console
 
-    $ py.test
+    $ pytest
     ...
     62746 passed in 220.43 seconds