Add tests for Python 3.8

Author: marv

.appveyor.yml

@@ -16,6 +16,8 @@ environment:
   - TOXENV: "py37-pytest30"
   - TOXENV: "py37-pytest31"
   - TOXENV: "py37-pytest4"
+  - TOXENV: "py38-pytest31"
+  - TOXENV: "py38-pytest4"
 
 install:
   - echo Installed Pythons

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 # Skip py37-pytest29 as such a combination does not work (#192)
-envlist=py{27,34,35,36}-pytest{29,30,31,4},py37-pytest{30,31,4}
+envlist=py{27,34,35,36}-pytest{29,30,31,4},py37-pytest{30,31,4},py38-pytest{31,4}
 
 [testenv]
 commands=