guix: add foo-dogsquared to meta.maintainers

pkgs/by-name/gu/guix/package.nix

···
     homepage = "http://www.gnu.org/software/guix";
     license = licenses.gpl3Plus;
     mainProgram = "guix";
-    maintainers = with maintainers; [ cafkafk ];
+    maintainers = with maintainers; [ cafkafk foo-dogsquared ];
     platforms = platforms.linux;
   };
 }