Support and Test against Python3.8

.gitlab-ci.yml

@@ -7,20 +7,25 @@ before_script:
 - pip install wheel tox
 
 test-3.5:
-  image: python:3.5-stretch
+  image: python:3.5-buster
   script:  
   - tox -e py35
 
 test-3.6:
-  image: python:3.6-stretch
+  image: python:3.6-buster
   script:  
   - tox -e py36
 
 test-3.7:
-  image: python:3.7-stretch
+  image: python:3.7-buster
   script:  
   - tox -e py37
 
+test-3.8:
+  image: python:3.8-buster
+  script:  
+  - tox -e py38
+
 deploy_production:
   stage: deploy
   image: python:3.6-stretch