message: add source-map
diff: @@ -5,7 +5,7 @@ const webpack = require('webpack');
  const WebpackDevServer = require('webpack-dev-server');
  new WebpackDevServer(webpack({
  - devtool: 'eval',
  + devtool: 'cheap-module-source-map',
  entry: [
  'webpack-dev-server/client?http://localhost:5000',
  'webpack/hot/only-dev-server',
  