basefiles: Reword sysupgrade message

sysupgrade 'upgrade' message more verbose than needs be.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

package/base-files/files/sbin/sysupgrade

@@ -267,7 +267,7 @@ fi
 run_hooks "" $sysupgrade_pre_upgrade
 
 install_bin /sbin/upgraded
-v "Commencing upgrade. All shell sessions will be closed now."
+v "Commencing upgrade. Closing all shell sessions."
 
 COMMAND='. /lib/functions.sh; include /lib/upgrade; do_upgrade_stage2'