IE11 needs a Promise polyfill for React 16.7

[Kazimirkas]

IE11 needs a Promise polyfill for React 16.7.
If you are using Lazy and Suspense feature, IE throws a null error. In 'readLazyComponentType' function implementation.

This is the bug example (comment out the Promise and it will work in IE 11)

https://codesandbox.io/s/7z37jwm5jj

If this issue will be confirmed, I would be proud to get my PR accepted for the documentation https://github.com/reactjs/reactjs.org/blob/master/content/docs/reference-javascript-environment-requirements.md?fbclid=IwAR3i6PnqPmLG_MUVk4IQXffXrMlvBchlb9UdA2BeXq_VDQJ9fMh8DoFPSJA
to extend the list of required polyfills
:)