Mark conflict between different versions of the multiple packages

Author: raphael-proust

packages/json-data-encoding/json-data-encoding.1.0.0/opam

@@ -24,6 +24,9 @@ depends: [
   "js_of_ocaml-compiler" { with-test }
   "conf-npm" { with-test }
 ]
+conflicts: [
+  "data-encoding" {!= version}
+]
 url {
   src:
     "https://gitlab.com/nomadic-labs/data-encoding/-/archive/v1.0.0/data-encoding-v1.0.0.tar.gz"