Upgrade Docker image

.gitlab-ci.yml

@@ -21,9 +21,9 @@ default:
     - exec-dind
   # see https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#tls-enabled
   # for image usage and settings for building with TLS and docker in docker
-  image: docker:19.03.1
+  image: docker:20.10.12
   services:
-    - docker:19.03.1-dind
+    - docker:20.10.12-dind
   variables:
     DOCKER_TLS_CERTDIR: "/certs"