opam show --raw --field without quotes

[kit-ty-kate]

For use in scripts, it would be nice to return values returned by opam show --raw --field without any qutotes.

For example opam show --raw -f url.src ppxlib returns:

"https://github.com/ocaml-ppx/ppxlib/releases/download/0.32.0/ppxlib-0.32.0.tbz"

and it would be nice if it returned

https://github.com/ocaml-ppx/ppxlib/releases/download/0.32.0/ppxlib-0.32.0.tbz