doc: update fs.utimes{,Sync} changelog

Specify that `NaN`, `Infinity`, and `-Infinity` are no longer valid
values for the `atime` and `mtime` arguments.

PR-URL: https://github.com/nodejs/node/pull/15680
Fixes: https://github.com/nodejs/node/issues/15453


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>