old_contents: const path = require('path');
  const babel = require('./babel');
  
  module.exports = () => ({
    ...babel({
      es: false,
      esnext: false,
      node: false
    }),
    ...{
      'config/babel.umd.js': () => {
        return {
          presets: [['env', { modules: false }], 'flow', 'react', 'stage-0']
        };
      },
      '.gitignore': ['/umd'],
      'package.json': {
        browser: 'umd/index.js',
        devDependencies: {
          rollup: '^0.49.3',
          'rollup-plugin-babel': '^3.0.2',
          'rollup-plugin-uglify': '^2.0.1'
        },
        files: ['umd/'],
        scripts: {
          'build:umd': 'rollup -c && rollup -c --min'
        }
      },
      'rollup.config.js': () => {
        const babel = require('rollup-plugin-babel');
        const babelConfig = require(path.join(process.cwd(), 'config/babel.umd'));
        const uglify = require('rollup-plugin-uglify');
        const yargs = require('yargs');
        const { min } = yargs.argv;
        return {
          input: 'src/index.js',
          output: {
            file: `umd/index${min ? '.min' : ''}.js`,
            format: 'umd'
          },
          plugins: [babel(babelConfig)].concat(min ? uglify() : []),
          sourcemap: true
        };
      }
    }
  });
  
new_contents: const { merge } = require('lodash');
  const path = require('path');
  const babel = require('./babel');
  
  module.exports = () =>
    merge(
      babel({
        es: false,
        esnext: false,
        node: false
      }),
      {
        'config/babel.umd.js': () => {
          return {
            presets: [['env', { modules: false }], 'flow', 'react', 'stage-0']
          };
        },
        '.gitignore': ['/umd'],
        'package.json': {
          browser: 'umd/index.js',
          devDependencies: {
            rollup: '^0.49.3',
            'rollup-plugin-babel': '^3.0.2',
            'rollup-plugin-uglify': '^2.0.1'
          },
          files: ['umd/'],
          scripts: {
            'build:umd': 'rollup -c && rollup -c --min'
          }
        },
        'rollup.config.js': () => {
          const babel = require('rollup-plugin-babel');
          const babelConfig = require(path.join(
            process.cwd(),
            'config/babel.umd'
          ));
          const uglify = require('rollup-plugin-uglify');
          const yargs = require('yargs');
          const { min } = yargs.argv;
          return {
            input: 'src/index.js',
            output: {
              file: `umd/index${min ? '.min' : ''}.js`,
              format: 'umd'
            },
            plugins: [babel(babelConfig)].concat(min ? uglify() : []),
            sourcemap: true
          };
        }
      }
    );
  
subject: Fix for rollup config.