Merge pull request #5816 from storybooks/fix/official-example-iframe

FIX build-storybook with simplebar esm files

lib/core/src/server/preview/iframe-webpack.config.js

@@ -81,7 +81,6 @@ export default ({
     resolve: {
       extensions: ['.mjs', '.js', '.jsx', '.json'],
       modules: ['node_modules'].concat(raw.NODE_PATH || []),
-      mainFields: ['browser', 'main', 'module'],
       alias: {
         'core-js': path.dirname(require.resolve('core-js/package.json')),
         ...reactPaths,