Update version constraint on Dune

Changed in 35cf29d.

Author: Julow

odoc.opam

@@ -29,7 +29,7 @@ depends: [
   "astring"
   "cmdliner" {>= "1.0.0"}
   "cppo" {build & >= "1.1.0"}
-  "dune" {>= "2.9.1"}
+  "dune" {>= "3.0.2"}
   "fpath"
   "ocaml" {>= "4.02.0"}
   "result"