syntax fixes

modules/home/services/nix-index/default.nix

@@ -29,10 +29,10 @@ in {
               coreutils
             ];
             text = ''
-              filename="index-$(uname -m | sed 's/^arm64$/aarch64/')-$(uname | tr A-Z a-z)"
+              filename="index-$(uname -m | sed 's/^arm64$/aarch64/')-$(uname | tr [:upper:] [:lower:])"
               mkdir -p ~/.cache/nix-index && cd ~/.cache/nix-index
               wget -q -N https://github.com/nix-community/nix-index-database/releases/latest/download/$filename
-              ln -f $filename files
+              ln -f "$filename" files
             '';
           }
         );