title: tag $ref don't show content openapi3.0
body: <p>I have this piece of the spec to api, with about content in an external file:</p>
  
  <pre><code>paths:
    /about:
      $ref: ./api/about.yml#/about
  </code></pre>
  
  <p>In this way, <code>about</code> content doesn't load when I make a bundle using <a href="https://pypi.org/project/openapi-cli-tool/" rel="nofollow noreferrer">openapi-cli-tool</a>. But, if I increase one auxiliar tag, the content is loaded.</p>
  
  <pre><code>paths:
    /about:
      whatever:
        $ref: ./api/about.yml#/about
  </code></pre>
  
  <p>Using the <code>whatever</code> tag, the Swagger Editor show a Structural error, but without her don't load. Some tips?</p>
  
  <p>Obs: I already saw some errors in the <code>$ref</code> tag in the openapi 3.0.</p>