addons: fix paths to shell

Signed-off-by: Joel Fernandes (Google) <joelaf@google.com>
diff --git a/addons/build-debian-tar b/addons/build-debian-tar
index ce7a753..2c58c37 100755
--- a/addons/build-debian-tar
+++ b/addons/build-debian-tar
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/system/bin/sh
 set -e
 # Build a tarball out of a android environment which I can then
 # upload to places for people who want to expedite the install
diff --git a/addons/device-umount-all b/addons/device-umount-all
index f68aac7..fe3b092 100755
--- a/addons/device-umount-all
+++ b/addons/device-umount-all
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/system/bin/sh
 
 if [ "$1x" == "--debugx" ]; then
 	set -x