simplify bumpr usage to make release process easier

Author: ziirish

bumpr.rc

@@ -4,7 +4,7 @@ vcs = git
 commit = true
 tag = true
 push = true
-tests = tox
+tests = tox -e py38
 clean =
     inv clean
 files =

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py{27,34,35,36,37}, pypy, pypy3, doc
+envlist = py{27,35,36,37,38}, pypy, pypy3, doc
 
 [testenv]
 commands = {posargs:inv test qa}