[wp/why3] try why3 version 1.1.1

nix/default.nix

@@ -150,7 +150,7 @@ rec {
         name = "frama-c-wp-qualif";
         buildInputs = mk_buildInputs { opamPackages = [
                     { name = "alt-ergo"; constraint = "=2.0.0"; }
-                    { name = "why3" ; constraint = "=1.2.0"; }
+                    { name = "why3" ; constraint = "=1.1.1"; }
                ]; };
         build_dir = main.build_dir;
         src = main.build_dir + "/dir.tar";