Fixed kaniko example to work after new kaniko release

doc/ci/docker/using_kaniko.md

@@ -60,6 +60,7 @@ build:
     name: gcr.io/kaniko-project/executor:debug
     entrypoint: [""]
   script:
+    - mkdir -p /kaniko/.docker
     - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
     - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
   only: