omni: change branch refs to 13.0

Change-Id: I07996ea076918aae2868a3e8c82d3920d9ab5b0f
diff --git a/prebuilt/common/bin/backuptool_ab.functions b/prebuilt/common/bin/backuptool_ab.functions
index 919fc4f..c0fbf5c 100644
--- a/prebuilt/common/bin/backuptool_ab.functions
+++ b/prebuilt/common/bin/backuptool_ab.functions
@@ -5,7 +5,7 @@
 
 export S=/system
 export C=/postinstall/tmp/backupdir
-export V=12
+export V=13
 export backuptool_ab=true
 
 copy_file() {