Update packages/hashset/hashset.1.0.0/opam

Author: mseri

packages/hashset/hashset.1.0.0/opam

@@ -16,7 +16,7 @@ remove: [
   ["ocamlfind" "remove" "hashset"]
 ]
 depends: [
-  "ocaml"
+  "ocaml" {< "5.0.0"}
   "ocamlfind"
   "obuild" {build & >= "0.1"}
 ]