add docker infra

.travis.yml

@@ -1,7 +1,10 @@
+sudo: required
 group: stable
 dist: xenial
 os: linux
 language: python
+services:
+  - docker
 python:
   - '2.7'
   - '3.5'
@@ -14,7 +17,8 @@ before_script:
   - pip install flake8 flake8-import-order
   # stop the build if there are Python syntax errors or undefined names
   - flake8 --count --application-import-names cowrie --max-line-length=120 --statistics .
-script: PYTHONPATH=${TRAVIS_BUILD_DIR}/src trial cowrie
+script:
+  -  PYTHONPATH=${TRAVIS_BUILD_DIR}/src trial cowrie
 notifications:
   email: false
   slack: