old_contents: 'use strict'
  
  const rollup = require('rollup')
  const babel = require('rollup-plugin-babel')
  const filesize = require('rollup-plugin-filesize')
  
  rollup.rollup({
    entry: 'src/index.js',
    plugins: [
      babel({
        exclude: 'node_modules/**',
        presets: ['es2015-rollup']
      }),
      filesize()
    ]
  }).then((bundle) => {
    console.log('server.js: ')
    bundle.write({
      format: 'iife',
      banner: '#!/usr/bin/env node',
      dest: 'server.js'})
  })
  
new_contents: import babel from 'rollup-plugin-babel'
  import filesize from 'rollup-plugin-filesize'
  
  export default {
    entry: 'src/index.js',
    dest: 'server.js',
    format: 'iife',
    banner: '#!/usr/bin/env node',
    plugins: [
      babel({
        exclude: 'node_modules/**',
        presets: ['es2015-rollup']
      }),
      filesize()
    ]
  }
  
subject: simplify rollup config file