title: How exclude !Ref tag from check-yaml git hook?
body: <p>There is a <code>serverless.yaml</code> file which contains line like that:</p>
  
  <pre><code>VpcId: !Ref MyVpc
  </code></pre>
  
  <p>Yaml files are validated by <code>check-yaml</code> <code>git</code> hook which invoked by <code>pre-commit</code> command. So the <code>pre-commit run --all-files</code> run is failed with error:</p>
  
  <pre><code>could not determine a constructor for the tag '!Ref'
    in "serverless.yml", line 172, column 29
  </code></pre>
  
  <p>Is there a way to configure <code>check-yaml</code> to skip this error?</p>