Update gnome-icon-theme to 3.12.0

After this version, gnome-icon-theme is merged with
gnome-icon-theme-symbolic and renamed to adwaita-icon-theme.

3.11.92
  - semi starred icon (bug #689098)
  - better fir for Files and save/open icons
  - addon and repositories icons (bug #724669)

3.11.5
  - scale gedit properly
  - media-player cleanup
  - make folder-download emblem more legible

(prlw1)