shorter image id, and use docker stable image

.gitlab-ci.yml

-image: docker:19.03.1
+image: docker:stable
 
 stages:
 - build
@@ -11,6 +11,7 @@ build:
   script:
     - docker pull $CI_REGISTRY_IMAGE:latest || true
     - docker build --cache-from $CI_REGISTRY_IMAGE:latest
-      --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA --tag $CI_REGISTRY_IMAGE:latest .
-    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+      --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA --tag $CI_REGISTRY_IMAGE:latest .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA
     - docker push $CI_REGISTRY_IMAGE:latest
+