Update settings of favonia/cloudflare-ddns

[favonia]

Thanks for using my DDNS updater. Since version 1.13.0 released on 16 July, the updater has stopped dropping superuser privileges by itself, instead relying on Docker's built-in mechanism to drop those privileges. The new way is safer and more reliable, but it made the old Docker template (which grants SETUID and SETGID) potentially less secure. I am on a mission to eliminate the old template from the internet. Please help me promote security best practices!

For more information about this design change, please read the CHANGELOG. If copyright ever matters, this PR itself is licensed under CC0, which should allow you to do whatever you want. Thank you again for your interest in my DDNS updater.

PS: You might see warnings about PUID and PGID being ignored from the new updater.

[trjohnson19]

@favonia, thanks for the proactive PR, and thank you for being generous with the CC0 license. Your image is great. I've incorporated your change!