cairo reverted to previous version in CorePure64

[Juanito]

cairo has been reverted to the previous version (1.17.2 -> 1.15.8 ) in the CorePure64 11.x repo.

This has fixed problems with:

* gedit and nautilus not starting in wayland sessions (gnome-session, weston)
* webkitgtk4 not loading https pages in wayland and x11 
* check boxes being unreadable in gtk3 apps

..the problem with distorted scalable icons in gtk3 apps remains