builder: set compression to 3

on omap5:

xz -z -1
641.9 MiB / 3,700.0 MiB = 0.173   4.8 MiB/s      12:56

xz -z -2
626.6 MiB / 3,700.0 MiB = 0.169   4.1 MiB/s      15:05

xz -z -3
609.3 MiB / 3,700.0 MiB = 0.165   3.5 MiB/s      17:48

xz -z -4
584.9 MiB / 3,700.0 MiB = 0.158   2.2 MiB/s      28:02

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

publish/bb.org_4gb_stable.sh

@@ -20,7 +20,7 @@ if [ -d ./deploy/${debian_lxde_4gb_stable} ] ; then
 	if [ -f bone-${debian_lxde_4gb_stable}-4gb.img ] ; then
 		mv bone-${debian_lxde_4gb_stable}-4gb.img ../
 		cd ../
-		xz -z -1 -v bone-${debian_lxde_4gb_stable}-4gb.img
+		xz -z -3 -v bone-${debian_lxde_4gb_stable}-4gb.img
 
 		rm -rf ./deploy/${debian_lxde_4gb_stable}/ || true
 	fi