ecwolf: make sure that a tag is fetched

Before this change, ecwolf.src.rev was set to the name of a tag. This is
generally not recommended. It’s better to set rev to
"refs/tags/<tag-name>" [1].

[1]: <https://nixos.org/manual/nixpkgs/stable/#fetchgit>

pkgs/by-name/ec/ecwolf/package.nix

@@ -25,7 +25,7 @@ stdenv.mkDerivation (finalAttrs: {
   src = fetchFromBitbucket {
     owner = "ecwolf";
     repo = "ecwolf";
-    rev = finalAttrs.version;
+    rev = "refs/tags/${finalAttrs.version}";
     sha256 = "V2pSP8i20zB50WtUMujzij+ISSupdQQ/oCYYrOaTU1g=";
   };