我用node:8.4.0作为我的主要形象。它将在其他工作中执行Node.js编程，我将在下面忽略它们。
这是我的.gitlab-ci.yml：
image: node:8.4.0
services:
- docker:latest
stages:
- docker_build
docker_build_job:
stage: docker_build
script:
- sudo docker build -t my_name/repo_name .
- sudo docker images
我无法在GitLab runner中使用docker命令，并收到以下消息：
Running with gitlab-ci-multi-runner 9.5.0 (413da38)
on ci server running on a VM of PEM5208 (5a0ceca0)
Using Docker executor with image node:8.4.0 ...
Starting service docker:latest ...
Pulling docker image docker:latest ...
Using docker image docker:latest ID=sha256:be47faef67c2e5950a540799e72189867b517010ad8ef98aa0181878d81b0064 for docker service...
Waiting for services to be up and running...
*** WARNING: Service runner-5a0ceca0-project-129-concurrent-0-docker-0 probably didn't start properly.
exit code 1
*********
Using docker image sha256:3f7a536cd71bb3049cc0aa12fb3e131a03a33efe2175ffbb95216d264500d1a1 for predefined container...
Pulling docker image node:8.4.0 ...
Using docker image node:8.4.0 ID=sha256:60bea5b8607945a43b53f5022088a73f2817174e11a3b20f78ea78a45f545d34 for build container...
Running on runner-5a0ceca0-project-129-concurrent-0 via ci...
Fetching changes...
Removing node_modules/
HEAD is now at 472e1e4 Change the version of docker image.
From https://here-is-my-domain/my_name/repo_name
472e1e4..df29530 master -> origin/master
Checking out 472e1e45 as master...
Skipping Git submodules setup
Downloading artifacts for build_installation_job (914)...
Downloading artifacts from coordinator... ok id=914 responseStatus=200 OK token=fMsaFRzG
$ docker build -t my_name/repo_name .
/bin/bash: line 48: docker: command not found
ERROR: Job failed: exit code 1
如何修改gitlab-ci的YAML文件，使其成功运行？