Relax lower bound on dune

Reported by Marcello Seri.

dune-project

@@ -16,7 +16,7 @@
  (synopsis "Code transformers for clangml")
  (depends
   (ocaml (and (>= 4.03.0) (< 4.12.0)))
-  (dune (>= 2.2.0))
+  (dune (>= 1.11.0))
   (clangml (>= 4.1.0))
   (dolog (>= 4.0.0))
   (traverse (>= 0.2.0))