Update readme with current test status

Looks like the tox setup is already testing python 3.5/3.6

Author: jeffwidman

README.txt

@@ -63,7 +63,7 @@ from this page.
 Python Versions
 ===============
 
-virtualenvwrapper is tested under Python 2.6 - 3.4.
+virtualenvwrapper is tested under Python 2.6 - 3.6.
 
 =======
 Support