fix warning with re.1.9.0

Author: vbmithr

cohttp.opam

@@ -34,7 +34,7 @@ bug-reports: "https://github.com/mirage/ocaml-cohttp/issues"
 depends: [
   "ocaml" {>= "4.04.1"}
   "dune" {build & >= "1.1.0"}
-  "re" {>= "1.7.2"}
+  "re" {>= "1.9.0"}
   "uri" {>= "2.0.0"}
   "fieldslib"
   "sexplib0"

cohttp/src/header.ml

@@ -173,7 +173,7 @@ let media_type_re =
 let get_first_match _re s =
   try
     let subs = Re.exec ~pos:0 media_type_re s in
-    let (start, stop) = Re.get_ofs subs 1 in
+    let (start, stop) = Re.Group.offset subs 1 in
     Some (String.sub s start (stop - start))
   with Not_found -> None