test on 3.8-dev

.travis.yml

@@ -67,6 +67,9 b' matrix:'
     - python: "3.7"
       dist: xenial
       sudo: true
+    - python: "3.8-dev"
+      dist: xenial
+      sudo: true
     - python: "3.7-dev"
       dist: xenial
       sudo: true