Travis CI: Add Python 3.8 to testing

Author: cclauss

.travis.yml

@@ -1,16 +1,7 @@
-sudo: false
+os: linux
+dist: focal
 language: python
 
-install:
-- pip install jupyter
-- pip install tox
-- pip install nbval
-- pip install pytest
-
-
-stages:
- - test
-
 jobs:
  include:
  - python: 3.5
@@ -19,8 +10,8 @@ jobs:
  env: TOXENV=py36
  - python: 3.7
  env: TOXENV=py37
-  dist: xenial
- sudo: true
+ - python: 3.8
+ env: TOXENV=py38
 
-script:
-- tox
+install: pip install jupyter nbval pytest tox
+script: tox