omni: update version for backupttool

Change-Id: I4974ac92151390fd8cc8e2c26f6b1bad60229a07
diff --git a/prebuilt/bin/backuptool.sh b/prebuilt/bin/backuptool.sh
index 19578b6..45a14e1 100755
--- a/prebuilt/bin/backuptool.sh
+++ b/prebuilt/bin/backuptool.sh
@@ -5,7 +5,7 @@
 
 export C=/tmp/backupdir
 export S=/system
-export V=8.0
+export V=8.1
 
 DEBUG=0