[nix] upgrade to coq 8.11.1

nix/default.nix

@@ -4,7 +4,7 @@
 let mk_buildInputs = { opamPackages ? [], nixPackages ? [] } :
     [ pkgs.gnugrep pkgs.gnused  pkgs.autoconf pkgs.gnumake pkgs.gcc pkgs.ncurses pkgs.time pkgs.python3 pkgs.perl pkgs.file] ++ nixPackages ++ opam2nix.build {
            specs = opam2nix.toSpecs ([ "ocamlfind" "zarith" "ocamlgraph" "yojson"
-                { name = "coq"; constraint = "=8.10.2";  }
+                { name = "coq"; constraint = "=8.11.1";  }
                 { name = "why3" ; constraint = "=1.3.1"; }
                 { name = "why3-coq" ; constraint = "=1.3.1"; }
                 { name = "menhir"; constraint = "=20190924"; }

src/plugins/wp/tests/wp_plugin/oracle_qualif/config.res.oracle

@@ -3,5 +3,5 @@ WP Requirements for Qualif Tests (3)
 ----------------------------------------------------------
 1. The Alt-Ergo theorem prover, version 2.3.0
 2. The Why3 platform, version 1.3.1
-3. The Coq Proof Assistant, version 8.11.0
+3. The Coq Proof Assistant, version 8.11.1
 ----------------------------------------------------------