dconf-editor
/org/gnome/desktop/input-sources/xkb-options
['ctrl:nocaps', 'caps:none']
Alternatively, you can use this command:
dconf write /org/gnome/desktop/input-sources/xkb-options "['caps:none', 'ctrl:nocaps']"
Both of these solutions will disable killing the X-Server with Ctrl+Alt+Backspace, but who wants that anyway? If you do, just add ['terminate:ctrl_alt_bksp']
back into the array
Put the above command in /etc/rc.local
or add a cron entry for it @reboot