Update opam file following removal of Stdlib dep

Author: proux01

coq-mathcomp-multinomials.opam

@@ -8,7 +8,8 @@ authors: ["Pierre-Yves Strub"]
 build: [make "-j%{jobs}%"]
 install: [make "install"]
 depends: [
-  "coq"                    {(>= "8.18" & < "8.21~") | = "dev"}
+  ("coq" {>= "8.18" & < "8.21~"}
+  | "rocq-core" {>= "9.0" | = "dev"})
   "coq-mathcomp-ssreflect" {(>= "2.0" & < "2.4~") | = "dev"}
   "coq-mathcomp-algebra"
   "coq-mathcomp-bigenough" {(>= "1.0" & < "1.1~") | = "dev"}