nixos/writefreely: fix admin user creation on sqlite

nixos/modules/services/web-apps/writefreely.nix

···
     withConfigFile ''
       query () {
         local result=$(${sqlite}/bin/sqlite3 \
-          '${cfg.stateDir}/${settings.database.filename}'
+          '${cfg.stateDir}/${settings.database.filename}' \
           "$1" \
         )