fix: change Access-Control-Allow-Headers to Access-Control-Expose-Headers in the readme

[ympek]

There is an error in the readme - incorrectly stating that the cross-origin server has to provide Access-Control-Allow-Headers, where the header we want is Access-Control-Expose-Headers

The HTTP Access-Control-Expose-Headers response header allows a server to indicate which response headers should be made available to scripts running in the browser in response to a cross-origin request.

I've also deleted the now-obsolete info about Safari not supporting the header

Best regards,
ympek

[nolanlawson]

D'oh! Thanks a bunch. Easy to mix these up. 😅