Add upper-bound on old merlin reader lib dependency

Author: voodoos

packages/dot-merlin-reader/dot-merlin-reader.4.6/opam

@@ -13,7 +13,7 @@ build: [
 depends: [
   "ocaml" {>= "4.08"}
   "dune" {>= "2.9.0"}
-  "merlin-lib" {>= "4.6"}
+  "merlin-lib" {>= "4.6" & < "4.9"}
   "ocamlfind" {>= "1.6.0"}
 ]
 description: