More fmt constraints

Author: dbuenzli

packages/current/current.0.5/opam

@@ -19,7 +19,7 @@ bug-reports: "https://github.com/ocurrent/ocurrent/issues"
 depends: [
   "ocaml" {>= "4.08.0"}
   "current_incr" {= version}
-  "fmt" {>= "0.8.9"}
+  "fmt" {>= "0.8.9" & < "0.10.0"}
   "bos"
   "ppx_deriving"
   "lwt" {>= "4.3.0"}