.gitlab-ci.yml: use base64 for username/password

https://gitlab.com/guided-explorations/containers/kaniko-docker-build

.gitlab-ci.yml

@@ -14,5 +14,5 @@ build:
     name: gcr.io/kaniko-project/executor:debug
     entrypoint: [""]
   script:
-    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
+    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"auth\":\"$(echo -n $CI_REGISTRY_USER:$CI_REGISTRY_PASSWORD | base64)\"}}}" > /kaniko/.docker/config.json
     - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA --destination $CI_REGISTRY_IMAGE:latest