Replace Anubis theme to prevent future issues

[gbraad]

Yes, today is the day I’m done with Anubis theme. It is no longer maintained, but it still works.

Ref: #21, https://mitrich.me/en/posts/anubis-closed/

[cfergeau]

https://github.com/zero-iee/hugo-theme-anubis-zero might work with newer hugo versions