Error using docker image on Gitlab

Describe the bug When running with the docker image on Gitlab, it throws an error saying

Unknown arguments: c, sh

To Reproduce

I have the config set up as follows:

stages:
  - lint

lint:
  stage: lint
  image: stoplight/spectral
  script:
    - spectral lint ./*.yaml

Expected behavior it Shoudn’t crash

Environment (remove any that are not applicable):

• Giltab runner version : 12.1.0

Additional context Here’s the whole log

Running with gitlab-runner 12.1.0 (de7731dd)
  on Autoscalling runner 8a6fef31
Using Docker executor with image stoplight/spectral ...
Pulling docker image stoplight/spectral ...
Using docker image sha256:1138f1564cd3ae6b28b639d00b4ecde1f7c1013436f76fd8622b07c5892790a2 for stoplight/spectral ...
Running on runner-8a6fef31-project-661-concurrent-0 via runner-8a6fef31-gitlab-docker-machine-1590659054-9111b302...
Fetching changes with git depth set to 50...
Initialized empty Git repository in [REDACTED]
Created fresh repository.
From [REDACTED]
 * [new ref]         refs/pipelines/9489 -> refs/pipelines/9489
 * [new branch]      develop             -> origin/develop
Checking out 8d691582 as develop...

Skipping Git submodules setup
spectral <command>

Commands:
  spectral lint [documents..]  lint JSON/YAML documents from files or URLs

Options:
  --version  Show version number  [boolean]
  --help     Show help  [boolean]

Unknown arguments: c, sh
ERROR: Job failed: exit code 1

[hpatoio]

I stumbled into this issue too. After reading here https://gitlab.com/gitlab-org/gitlab-runner/-/issues/2692#note_50147081 I was able to successfully use the official image with this yml

stages:
  - validate

validate_open-api:
  stage: validate
  image:
    name: stoplight/spectral
    entrypoint: [""]
  script:
   - spectral lint open-api.json

[nulltoken]

@hpatoio Awesome!

Would you feel like sharing this more widely and open a PR to update /docs/getting-started/2-installation.md?