Relax upper bound of Yojson < 2.0.0

Author: Niols

packages/morbig/morbig.0.11.0/opam

@@ -28,7 +28,7 @@ depends: [
   "odoc"                 {with-doc}
   "ppx_deriving_yojson"
   "visitors"             {>= "20200207"}
-  "yojson"               {>= "1.6.0" & < "2.0.0"}
+  "yojson"               {>= "1.6.0"}
   "conf-jq" {with-test}
 ]