Slim: Update backuptool for 5.1

Change-Id: Icc0cc4f0dbd4945cd3ed03e9975df8f2c5d83c51
diff --git a/prebuilt/common/bin/backuptool.functions b/prebuilt/common/bin/backuptool.functions
index 10d66a4..fe91f1f 100644
--- a/prebuilt/common/bin/backuptool.functions
+++ b/prebuilt/common/bin/backuptool.functions
@@ -5,7 +5,7 @@
 
 export C=/tmp/backupdir
 export S=/system
-export V=12
+export V=5.1
 
 backup_file() {
   if [ -e "$1" ]; then