Babel 6에서 Async/Await를 사용할 때 \'regeneratorRuntime이 정의되지 않았습니다\'라는 메시지가 나타나는 이유는 무엇입니까?

npm i -D babel-core babel-polyfill babel-preset-es2015 babel-preset-stage-0 babel-loader

"babel-polyfill": "^6.0.16"

{
  "presets": [ "es2015", "stage-0" ]
}

"use strict";

export default async function foo() {
  var s = await bar();
  console.log(s);
}

function bar() {
  return "bar";
}

require("babel-core/register");
require("babel-polyfill");

module.exports = {
  entry: ['babel-polyfill', './test.js'],

  output: {
    filename: 'bundle.js'       
  },

  module: {
    loaders: [
      { test: /\.jsx?$/, loader: 'babel', }
    ]
  }
};

mocha --compilers js:babel-core/register --require babel-polyfill