title: gitlab-ci.yaml `config contains unknown keys: rules` when trying to use rules
body: <p>I've pasted the example for rules in my gitlab-ci.yaml (from <a href="https://docs.gitlab.com/ee/ci/yaml/#rules" rel="nofollow noreferrer">https://docs.gitlab.com/ee/ci/yaml/#rules</a>):</p>
  <pre><code>job:
    script: &quot;echo Hello, Rules!&quot;
    rules:
      - if: '$CI_MERGE_REQUEST_TARGET_BRANCH == &quot;master&quot;'
        when: always
      - if: '$VAR =~ /pattern/'
        when: manual
      - when: on_success
  </code></pre>
  <p>But I get</p>
  <pre><code>Error: jobs:job config contains unknown keys: rules
  </code></pre>
  <p>Am I missing something?</p>