Add missing 'v'-prefix in catala's ppx_yojson_conv dependency bound

Author: jmid

packages/catala/catala.0.9.0/opam

@@ -31,7 +31,7 @@ depends: [
   "ocamlfind" {!= "1.9.5"}
   "ocamlgraph" {>= "1.8.8"}
   "yojson" {>= "2.0" }
-  "ppx_yojson_conv" {>= "0.14.0"}
+  "ppx_yojson_conv" {>= "v0.14.0"}
   "re" {>= "1.9.0"}
   "sedlex" {>= "2.4" & < "3.5"}
   "uutf" {>= "1.0.3"}