build: Require gsettings-desktop-schemas >= 3.13.91

This is required for new location panel, and the search panel whitelist.

https://bugzilla.gnome.org/show_bug.cgi?id=731119
https://bugzilla.gnome.org/show_bug.cgi?id=734108
privacy: Add location setting

For now its just a switch to enable/disable geolocation through
gnome-shell's setting. In future we'll hopefully at least have
controls to enable/disable geolocation for applications from here.

https://bugzilla.gnome.org/show_bug.cgi?id=731119