mathjs: Unexpected token in round.js

When upgrading to MathJS 6.0.2, we get an error when trying to make use of mathjs in our application, compiling with Webpack 3.4.0:

11:13:27 webpack.1           | ERROR in ./node_modules/mathjs/src/function/arithmetic/round.js
11:13:27 webpack.1           | Module parse failed: Unexpected token (58:4)
11:13:27 webpack.1           | You may need an appropriate loader to handle this file type.
11:13:27 webpack.1           | |    */
11:13:27 webpack.1           | |   const round = typed(name, {
11:13:27 webpack.1           | |     ...roundNumberSignatures,
11:13:27 webpack.1           | | 
11:13:27 webpack.1           | |     'Complex': function (x) {
11:13:27 webpack.1           |  @ ./node_modules/mathjs/src/factoriesAny.js 98:0-57
11:13:27 webpack.1           |  @ ./node_modules/mathjs/src/entry/mainAny.js
11:13:27 webpack.1           |  @ ./node_modules/mathjs/main/es6/index.js
11:13:27 webpack.1           |  @ ./app/javascript/src/config/math.ts

Here’s what it looks like where we set up MathJS:

import {
  create,
  addDependencies,
  BigNumberDependencies,
  divideDependencies,
  evaluateDependencies,
  multiplyDependencies,
  subtractDependencies,
} from 'mathjs';

// http://mathjs.org/docs/custom_bundling.html

const math = create([
  addDependencies,
  BigNumberDependencies,
  divideDependencies,
  evaluateDependencies,
  multiplyDependencies,
  subtractDependencies,
]);

export default math;