Include the new Google Books app in backuptool.sh

This app is part of the new Gapps from the GRI40 N1 update.
Try it with these Gapps I packaged for lack of a better source.

Change-Id: Ib49fd13e0270dfa15d5e05843a6f11f2b2d6388e
http://bit.ly/hfgtL0
diff --git a/prebuilt/common/bin/backuptool.sh b/prebuilt/common/bin/backuptool.sh
index cd3107b..3953b5e 100755
--- a/prebuilt/common/bin/backuptool.sh
+++ b/prebuilt/common/bin/backuptool.sh
@@ -27,6 +27,7 @@
 
 get_files() {
     cat <<EOF
+app/BooksPhone.apk
 app/CarHomeGoogle.apk
 app/CarHomeLauncher.apk
 app/Facebook.apk