Switch testing to Victoria testing runtime

Updating the testing template from ussuri to victoria
testing runtime
- https://governance.openstack.org/tc/reference/runtimes/victoria.html

Change-Id: If964909a73a52836e3adbb7b695f1c7322b81830
diff --git a/tox.ini b/tox.ini
index e861c84..0477d6f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = pep8,py36,py37,bashate,pip-check-reqs
+envlist = pep8,py36,py38,bashate,pip-check-reqs
 minversion = 3.1.1
 skipsdist = True
 ignore_basepython_conflict = True