fix(build): Require dolmen 0.9 (#1050)

We are not compatible with the development release of Dolmen due to the
`implicit` field added in [1]. Further, we currently require that Dolmen
move trigger annotations in SMT-LIB format from the body of the formula
to the quantifier itself, but this was removed in [2].

Since both of these will be part of the next release of dolmen, let us
pre-emptively ensure that release won't break Alt-Ergo.

[1] : Gbury/dolmen#199
[2] : Gbury/dolmen#207

dune-project

@@ -77,9 +77,9 @@ See more details on http://alt-ergo.ocamlpro.com/"
   (ocaml (>= 4.08.0))
   dune
   dune-build-info
-  (dolmen (>= 0.9))
-  (dolmen_type (>= 0.9))
-  (dolmen_loop (>= 0.9))
+  (dolmen (= 0.9))
+  (dolmen_type (= 0.9))
+  (dolmen_loop (= 0.9))
   (ocplib-simplex (>= 0.5))
   (zarith (>= 1.11))
   seq