Update opam metadata (#1386)
Update opam metadata (#1386)

* Update opam file from repository

See:
- ocaml/opam-repository#16528
- ocaml/opam-repository#16484

* Update minimum base version to 0.12.0

Due to `List.equal` we're actually only compatible with 0.12.0.
ocaml-ppx/ocamlformat,ocaml-ppx/ocamlformat,ocaml-ppx/ocamlformat