Merge pull request #268 from math-comp/fix-ci

Update config.nix

Author: gares

.nix/config.nix

@@ -6,7 +6,7 @@
       mathcomp.override.version = "hierarchy-builder";
       mathcomp.job = false;
       mathcomp-single.job = true;
-      coq-elpi.override.version = "master";
+      coq-elpi.override.version = "v1.11.1";
   }; in {
     "coq-8.13".coqPackages = {
       coq.override.version = "8.13";