Relax OCaml upper bound.

Author: xclerc

base.opam

@@ -11,7 +11,7 @@ build: [
   ["dune" "build" "-p" name "-j" jobs]
 ]
 depends: [
-  "ocaml"             {>= "4.04.2" & <= "4.08.0"}
+  "ocaml"             {>= "4.04.2" & < "4.09.0"}
   "sexplib0"          {>= "v0.12" & < "v0.13"}
   "dune"              {build & >= "1.5.1"}
 ]