Merge pull request #724 from common-workflow-language/no_py33

Confirm that we no longer support Python 3.3

Author: mr-c

README.rst

@@ -21,7 +21,7 @@ This is the reference implementation of the Common Workflow Language.  It is
 intended to feature complete and provide comprehensive validation of CWL
 files as well as provide other tools related to working with CWL.
 
-This is written and tested for Python ``2.7 and 3.x {x = 3, 4, 5, 6}``
+This is written and tested for `Python <https://www.python.org/>`_ ``2.7 and 3.x {x = 4, 5, 6}``
 
 The reference implementation consists of two packages.  The ``cwltool`` package
 is the primary Python module containing the reference implementation in the