Updated webpack.config.babel.js with '-loader'

webpack.config.babel.js

import webpack from 'webpack'

export default {
  entry: [
    'babel-polyfill',
    './src/index.js'
  ],

  output: {
    path: './dist',
    filename: 'index.js',
    chunkFilename: '[name].js'
  },

  module: {
    rules: [
      { test: /\.js$/, exclude: /node_modules/, loader: 'babel-loader' },
      { test: /\.css$/, loader: 'style-loader!css-loader!postcss-loader' },
      { test: /\.json$/, loader: 'json-loader' }
    ]
  },

  plugins: [
    // https://github.com/postcss/postcss-loader/issues/99
    new webpack.LoaderOptionsPlugin({
      test: /\.css$/,
      options: {
        postcss: (webpackInstance) => [
          require('postcss-import')({ addDependencyTo: webpackInstance }),
          require('precss')()
        ],
        context: __dirname,
      },
    }),
    ...process.env.NODE_ENV === 'production' ? [
      new webpack.LoaderOptionsPlugin({ minimize: false, debug: false }),
      new webpack.optimize.DedupePlugin(),
      new webpack.optimize.UglifyJsPlugin({
        compress: {
          warnings: false,
          screw_ie8: true,
          sequences: true,
          dead_code: true,
          drop_debugger: true,
          comparisons: true,
          conditionals: true,
          evaluate: true,
          booleans: true,
          loops: true,
          unused: true,
          hoist_funs: true,
          if_return: true,
          join_vars: true,
          cascade: true,
          drop_console: true
        },
        output: {
          comments: false
        }
      })
    ] : [],
  ]
}