ci: set docker as service

.gitlab-ci.yml

@@ -3,7 +3,8 @@ stages:
 
 build:
   stage: build
-  image: docker:18.09.6
+  services:
+    - docker:18.09.6-dind
   script:
     - ./build-plugins.sh
     - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN registry.e-biz.fr