Polyfill promises
Polyfill.io - service to provide support for older browsers.
It’s based on the browsers user agent. Different polyfills are served based on the browser.
Creates a general url to get the correct polyfill:
http://cdn.polyfill.io/v2/polyfill.min.js
Adds this URL in the index.html file. This will polyfill the promises API for the Webpack runtime, but only for browsers that don’t have already.