Travis-CI: add docker service

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>

.travis.yml

@@ -16,4 +16,9 @@ env:
 script:
   - make $TEST_SUITE
 
-sudo: false #docker containers for CI
+# For docker containers
+
+sudo: required
+
+services:
+  - docker