Webpack: build error converting a lib's ... spread operator to ES5?

index.js

// npm install && npm run build

// In output.js, spreadTest(...args) is converted to ES5
function spreadTest(...args) {
  return args;
}
console.log(spreadTest(1, 2, 3));

// But the ...args inside of this lib's "audit" function is NOT converted to ES5
import 'react-axe';

package.json

{
  "name": "webpack-react-axe",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "webpack"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "react-axe": "^1.0.6"
  },
  "devDependencies": {
    "babel-core": "^6.14.0",
    "babel-loader": "^6.2.5",
    "babel-preset-es2015": "^6.14.0",
    "webpack": "^1.13.2"
  }
}

webpack.config.js

var path = require('path');

module.exports = {
  entry: path.join(__dirname, 'index.js'),
  output: {
    path: __dirname,
    filename: 'output.js',
  },
  module: {
    loaders: [
      {
        test: /\.js$/,
        exclude: /(node_modules|bower_components)/,
        loader: 'babel',
        query: {
          presets: ['es2015'],
        },
      },
    ],
  },
};