added python 3.7 to travis CI

Author: gdementen

.travis.yml

@@ -8,6 +8,14 @@ python:
     - "3.5"
     - "3.6"
 
+# Work-around to enable python 3.7 without globally enabling sudo and dist: xenial for other build jobs
+# see https://github.com/travis-ci/travis-ci/issues/9815
+matrix:
+  include:
+    - python: 3.7
+      dist: xenial
+      sudo: true
+
 branches:
     only:
         - master