Fix molecule and testinfra version to make test pass => Need to migra…

…te them on testinfra > 1.19.0

.travis.yml

@@ -13,7 +13,7 @@ notifications:
 install:
   - pip install ansible==2.7.1
   - pip install funcsigs
-  - pip install molecule
+  - pip install molecule==2.20.1 testinfra==1.19.0
   - pip install docker-py
   - pip install flake8
   - pip install -r requirements.txt