Replace the vpnkit.opam symlink with a copy of the file
Replace the vpnkit.opam symlink with a copy of the file

Unfortunately on Windows symlinks only partially work, in particular
native Windows (i.e. native OCaml programs) don't understand them.
This causes `jbuilder build` to fail.

This patch duplicates the `vpnkit.opam` file so that it works properly
under Windows.

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

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit