also pass --root with the path to backup to the backupwordpress cmd

This is mainly to work around a bug in backupwordpress if home and
siteurl are not the same.

See xibodevelopment/backupwordpress#1162 for
technical details

files/scripts/upgrade_wordpress.sh

@@ -60,7 +60,7 @@ function wp_backup {
 
   echo "Making the backup..."
   # exclude the default backup path
-  run_wp_hard "backupwordpress backup --destination=${backup_dir} --excludes='wp-content/backupwordpress-*'"
+  run_wp_hard "backupwordpress backup --root=${wwwdir} --destination=${backup_dir} --excludes='wp-content/backupwordpress-*'"
   # only deactivate if we updated it
   # otherwise we assume the user has it activated and configured
   if [ $activate_backup -gt 0 ]; then