fix sedlex constraint

Author: Hugo Heuzard

packages/js_of_ocaml-compiler/js_of_ocaml-compiler.5.1.1/opam

@@ -17,7 +17,7 @@ depends: [
   "ppxlib" {>= "0.15.0"}
   "re" {with-test}
   "cmdliner" {>= "1.1.0"}
-  "sedlex"
+  "sedlex" {>= "2.3"}
   "menhir"
   "menhirLib"
   "menhirSdk"