change credentials directory from /kaniko/.docker to /root/.docker

Latest versions of Kaniko builder use this new credentials directory

.gitlab-ci.yml

@@ -25,8 +25,8 @@ variables:
     untracked: true
     expire_in: 1 hour
   before_script:
-    - mkdir -p /kaniko/.docker
-    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
+    - mkdir -p /root/.docker
+    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /root/.docker/config.json
 
 build-env:ubuntu:
   <<: *build-env