Require more recent dune.

refinedc.opam

@@ -18,7 +18,7 @@ dev-repo: "git+https://gitlab.mpi-sws.org/iris/refinedc.git"
 depends: [
   "coq" { (>= "8.11.0" & < "8.12~") | (= "dev") }
   "coq-iris" { (= "dev.2020-09-29.7.19ba2bc0") | (= "dev") }
-  "dune" {>= "2.0.0"}
+  "dune" {>= "2.7.0"}
   "cerberus" {= "~dev"}
   "cmdliner" {>= "1.0.4"}
   "earley" {= "2.0.0"}