message: fix: universal folder -> universal file
diff: import chalk from 'chalk';
  import fs from 'fs-extra';
  -import { relative as relativePath, join as joinPath } from 'path';
  +import { relative as relativePath } from 'path';
  import peerDepsExternal from 'rollup-plugin-peer-deps-external';
  import commonjs from '@rollup/plugin-commonjs';
  import resolve from '@rollup/plugin-node-resolve';
  @@ -85,13 +85,13 @@ export const makeConfigs = async (
  // to be bridge between
  // frontend- and backend-
  // plugins' code
  - const UNIVERSAL_FOLDER = 'universal';
  - const universalPath = paths.resolveTarget(UNIVERSAL_FOLDER);
  + const UNIVERSAL_FILE = 'universal.js';
  + const universalPath = paths.resolveTarget(UNIVERSAL_FILE);
  const universalFileExists = fs.existsSync(universalPath);
  if (universalFileExists) {
  - mainFields.push(UNIVERSAL_FOLDER);
  - commonjsInclude.push(joinPath(UNIVERSAL_FOLDER, '*.js'));
  + mainFields.push(UNIVERSAL_FILE);
  + commonjsInclude.push(UNIVERSAL_FILE);
  }
  configs.push({
  