Resync opam with mirage-dev
Resync opam with mirage-dev

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

samoht/ocaml-vchan,mirage/ocaml-vchan,djs55/ocaml-vchan,mirage/ocaml-vchan,djs55/ocaml-vchan,samoht/ocaml-vchan,samoht/ocaml-vchan,djs55/ocaml-vchan,mirage/ocaml-vchan