travis: add cmdliner
travis: add cmdliner

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

djs55/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs,djs55/ocaml-xen-lowlevel-libs,euanh/ocaml-xen-lowlevel-libs