More recent version of Menhir without warnings

Previous version generated a lot of warnings such as:

> Warning 9 [missing-record-field-pattern]: the following labels are not
> bound in this record pattern.

which break the compilation when used with a recent version of Dune.

Author: Niols

packages/morbig/morbig.0.11.0/opam

@@ -23,7 +23,7 @@ dev-repo: "git+https://github.com/colis-anr/morbig.git"
 
 depends: [
   "dune"                 {>= "2.5.0"}
-  "menhir"               {>= "20180538"}
+  "menhir"               {>= "20200211"}
   "ocaml"                {>= "4.11"}
   "odoc"                 {with-doc}
   "ppx_deriving_yojson"