Demo doesn't run in Internet Explorer

There are two known issues in Internet Explorer (IE):
1. IE [lacks native Promise support](https://caniuse.com/#search=promise), so you need to add a promise polyfill to get the demo to work in IE.

2. IE tries to download the JSON from the mock API at localhost:3001/users. [Here are some workarounds](https://stackoverflow.com/questions/6114360/ie-prompts-to-open-or-save-json-result-from-server).