Bump up python version of unit test

This commit bumps up the python version to 3.6. This change encourages
developers to use our latest python version on unit tests.

Change-Id: I45d79c90939aa0f743750fec4b4e286f3679563b
diff --git a/README.rst b/README.rst
index 0a130dc..307ceb3 100644
--- a/README.rst
+++ b/README.rst
@@ -198,21 +198,21 @@
 is ``test_path=./tempest/test_discover`` which will only run test discover on the
 Tempest suite.
 
-Alternatively, there are the py27 and py35 tox jobs which will run the unit
+Alternatively, there are the py27 and py36 tox jobs which will run the unit
 tests with the corresponding version of python.
 
 One common activity is to just run a single test, you can do this with tox
-simply by specifying to just run py27 or py35 tests against a single test::
+simply by specifying to just run py27 or py36 tests against a single test::
 
-    $ tox -e py27 -- -n tempest.tests.test_microversions.TestMicroversionsTestsClass.test_config_version_none_23
+    $ tox -e py36 -- -n tempest.tests.test_microversions.TestMicroversionsTestsClass.test_config_version_none_23
 
 Or all tests in the test_microversions.py file::
 
-    $ tox -e py27 -- -n tempest.tests.test_microversions
+    $ tox -e py36 -- -n tempest.tests.test_microversions
 
 You may also use regular expressions to run any matching tests::
 
-    $ tox -e py27 -- test_microversions
+    $ tox -e py36 -- test_microversions
 
 Additionally, when running a single test, or test-file, the ``-n/--no-discover``
 argument is no longer required, however it may perform faster if included.