Merge "Use py3 as the default runtime for tox"

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.1.0
-envlist = py38,py{36,38}-{zookeeper,redis,sentinel,memcached,postgresql,mysql,consul,etcd,etcd3,etcd3gw},pep8
+envlist = py3,py{36,38}-{zookeeper,redis,sentinel,memcached,postgresql,mysql,consul,etcd,etcd3,etcd3gw},pep8
 ignore_basepython_conflict = True
 
 [testenv]