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).

Start by running the demo in Internet Explorer and inspect how it loads the Promise-dependent code and requests JSON from the mock API at localhost:3001/users. Check the linked Promise support and JSON workaround references, then verify that the demo runs successfully in IE without the download prompt.

Written by the indexing model from the issue text.