Minimum OCaml version is now 4.13.0

Because of String.get_uint*_le

Author: xavierleroy

packages/camlzip/camlzip.1.12/opam

@@ -14,7 +14,7 @@ build: [
 ]
 install: [make "install"]
 depends: [
-  "ocaml" {>= "4.07.0"}
+  "ocaml" {>= "4.13.0"}
   "ocamlfind" {build}
   "conf-zlib"
 ]