title: How to use new automatic react runtime import with @mdx-js/loader
body: <p>I am using MDX with React's new <a href="https://reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html" rel="noreferrer">JSX Transform</a>. My babel configuration is following:</p>
  <pre><code>const plugins = [
    ['@babel/plugin-proposal-nullish-coalescing-operator'],
    ['@babel/plugin-proposal-optional-chaining'],
    ['@babel/plugin-transform-react-jsx', {
      runtime: 'automatic',
      importSource: 'react'
    }]
  ];
  </code></pre>
  <p>However when bundling and transpiling MDX files via Webpack using <code>@mdx-js/loader</code>, I get following error:</p>
  <pre><code>importSource cannot be set when runtime is classic.
  </code></pre>
  <p>It looks like it is not picking runtime as <code>automatic</code> from the <code>Babel</code> configuration. How can I tell the loader to pick import source as mentioned in the babel config file.</p>