travis docker fix

Author: k-florek

.travis.yml

@@ -3,6 +3,9 @@ python:
   - "3.6"
 services:
   - docker
+before_install:
+  # Upgrade Docker to work with docker-py.
+  - curl https://gist.githubusercontent.com/geerlingguy/ce883ad4aec6a5f1187ef93bd338511e/raw/36612d28981d92863f839c5aefe5b7dd7193d6c6/travis-ci-docker-upgrade.sh | sudo bash
 #install dependencies
 install:
   - pip install -r requirements.txt