Test against official python3.8 and use 3.7 for codestyle and deployment (#71)

Author: LKaemmerling

.travis.yml

@@ -11,7 +11,7 @@ python:
 - '3.5'
 - '3.6'
 - '3.7'
-- "3.8-dev"
+- '3.8'
 
 before_script:
 - docker pull lkdevelopment/hetzner-cloud-api-mock
@@ -24,17 +24,16 @@ install:
 - pip install tox-travis
 
 script: tox
-
 jobs:
   include:
     - stage: codingstyle
       env: STAGE=style_check
-      python: "3.6"
+      python: "3.7"
       script: tox -e flake8
     - stage: deploy
       env: STAGE=deploy
       if: tag IS present
-      python: "3.6"
+      python: "3.7"
       script: echo "Deploy to pypi"
       deploy:
         provider: pypi