add python v3.8 support to travis

Author: pqlMC

.travis.yml

@@ -10,6 +10,7 @@ matrix:
     env:
       # Do not run analysis on PR (secure env variables like SONAR_TOKEN are not always available)
       - WITH_SONAR_ANALYSIS=$([ "$TRAVIS_PULL_REQUEST" = "false" ] && echo true || echo false)
+  - python: "3.8-dev" # 3.8 final expected for Oct. 2019
 
 install:
   - pip3 install -r requirements.txt