security(minor): chmod 0700 ~/.config/duckdns.sh

When we create the directories we should change the permissions to be more strict.

```sh
chmod 0700 ~/.config/duckdns.sh
chmod 0600 ~/.config/duckdns.sh/*.env
```

In most cases people will use this on single-user systems, so it's not _that_ big of a deal, but it's a nice thing to do for when someone serves up their home directory, y'know.