Force Python Docker version for Travis.

WIP

WIP

.travis.yml

@@ -1,8 +1,8 @@
 ---
-language: python
-services: docker
+  language: python
+  services: docker
   
-env:
+  env:
     global:
       - ROLE_NAME: cloudflare-acme
     matrix:
@@ -13,23 +13,25 @@ env:
       - MOLECULE_DISTRO: debian9
       - MOLECULE_DISTRO: debian10
 
-install:
+  install:
     # Install test dependencies.
-  - pip install molecule docker testinfra ansible-lint flake8 yamllint
+    - pip install molecule docker==4.2.2 testinfra ansible-lint flake8 yamllint
   
-before_script:
+  before_script:
     # Use actual Ansible Galaxy role name for the project directory.
     - cd ../
     - mv ansible-$ROLE_NAME $ROLE_NAME
     - cd $ROLE_NAME
   
-script:
+  script:
+    - docker --version
     - molecule --version
     - ansible --version
     - molecule test
   
-notifications:
+  notifications:
     webhooks:
       urls:
         - "https://galaxy.ansible.com/api/v1/notifications/"
       on_success: change
+