omni: update version for OTA backup

Change-Id: I74cea2dff25b80e677654c44e92eef5f3a6f3e24
diff --git a/prebuilt/bin/backuptool.sh b/prebuilt/bin/backuptool.sh
index 85566e2..ce3627f 100755
--- a/prebuilt/bin/backuptool.sh
+++ b/prebuilt/bin/backuptool.sh
@@ -5,7 +5,7 @@
 
 export C=/tmp/backupdir
 export S=/system
-export V=7.1
+export V=8.0
 
 # Preserve /system/addon.d in /tmp/addon.d
 preserve_addon_d() {