fix: (useCopyToClipboard): copyToClipboard should return promise

[kendrickw]

Fixes #312

The copyToClipboard function is not returning a promise currently. The intention (at least according to the function signature) is to fulfill the promise when the text is copied: https://github.com/uidotdev/usehooks/blob/90fbbb4cc085e74e50c36a62a5759a40c62bb98e/index.d.ts#L126-L129

This PR will change the code to return a promise. So the promise can fulfill when the text is copied successfully.

[tresorama]

Please merge this.

Currently this other npm lib has a working version: https://usehooks-ts.com/react-hook/use-copy-to-clipboard

[Sparebola]

up