AppVeyor: pin Jbuilder to 1.0+beta16
AppVeyor: pin Jbuilder to 1.0+beta16

See https://github.com/ocaml/dune/issues/483.

ocsigen/lwt,rneswold/lwt,rneswold/lwt,c-cube/lwt,c-cube/lwt,c-cube/lwt,ocsigen/lwt,rneswold/lwt,ocsigen/lwt