Pin docker version for travis

.travis.yml

@@ -2,6 +2,15 @@
 services: docker
 language: python
 
+before_install:
+  - curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+  - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
+  - sudo apt-get update
+  - sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
+
+env:
+  - DOCKER_API_VERSION=1.38
+
 install:
   - pip3 install docker molecule==3.0.6 yamllint ansible-lint openshift jmespath