concord: change maintainer to sigmanificient

Signed-off-by: Emily Flion <[e-mail]>

pkgs/by-name/co/concord/package.nix

···
     homepage = "https://cogmasters.github.io/concord/";
     changelog = "https://github.com/Cogmasters/concord/releases/tag/v${finalAttrs.version}";
     license = lib.licenses.mit;
-    maintainers = with lib.maintainers; [ emneo ];
+    maintainers = with lib.maintainers; [ sigmanificient ];
     platforms = lib.platforms.unix;
   };
 })