make-disk-image.nix: Really fix write permissions in the store

I think the current one applies the -exec only to those that match
'-type d'. Let's switch it to something that humans can understand...

Changed files
+1 -1
nixos
+1 -1
nixos/lib/make-disk-image.nix
···
fakeroot nixos-prepare-root $root ${channelSources} ${config.system.build.toplevel} closure
# fakeroot seems to always give the owner write permissions, which we do not want
-
find $root/nix/store -mindepth 1 -maxdepth 1 -type f -o -type d -exec chmod -R a-w '{}' \;
+
find $root/nix/store -mindepth 1 -maxdepth 1 -type f -o -type d | xargs chmod -R a-w
echo "copying staging root to image..."
cptofs ${optionalString partitioned "-P 1"} -t ${fsType} -i $diskImage $root/* /