[scribus] Nightly for MacOS Mojave only (no more)

[Giovanni Bianchessi]

> 
> I am running macOS High Sierra 10.13.6 and Scribus Nightly 1.5.5 svn 22778 is working well.
> I can't upgrade to Mojave since my iMac is not compatible with it, since it is old.
> 
> Regards
> Giovanni Bianchessi
> 

Thank you!
I have had no time to test it deeply yet, but it seems to work well.

Regards
Giovanni