travis: correct the opam pin for conduit
travis: correct the opam pin for conduit

mor1/ocaml-cohttp,dsheets/ocaml-cohttp,edwintorok/ocaml-cohttp,Drup/ocaml-cohttp,edwintorok/ocaml-cohttp,dsheets/ocaml-cohttp,Drup/ocaml-cohttp,marklrh/ocaml-cohttp,edwintorok/ocaml-cohttp,fdopen/ocaml-cohttp,marklrh/ocaml-cohttp,inhabitedtype/ocaml-cohttp,inhabitedtype/ocaml-cohttp,mor1/ocaml-cohttp,fdopen/ocaml-cohttp,inhabitedtype/ocaml-cohttp,Drup/ocaml-cohttp,fdopen/ocaml-cohttp,dsheets/ocaml-cohttp,marklrh/ocaml-cohttp,mor1/ocaml-cohttp