Update OnRetryFunction type

[mikefowler]

Two updates to the OnRetryFunction type:

• Allow the onRetry function to return void
  • The return value defaults to an empty object (values = {}, on line ~103), so it makes sense that the method should be able to return nothing
• The documentation states that the onRetry method supports returning a Promise, but the TypeScript types had not been updated to reflect this

[elbywan]

@mikefowler Thanks a lot for the fixes! 👍

I just published 0.1.10 that includes the commit.

[mikefowler]

Thanks @elbywan!