findDOMNode is deprecated in StrictMode

When I select a file I'm receiving this error message in the Console when run in React StrictMode:

Warning: findDOMNode is deprecated in StrictMode

See also: https://reactjs.org/docs/strict-mode.html#warning-about-deprecated-finddomnode-usage

[zacjones93]

For those running into this issue, I solved this by updating react-s3-uploader to use a ref instead

https://github.com/skillrecordings/egghead-next/pull/1449/files