Fix missing tab in main config block

It appears this was accidently changed from a hard tab to two spaces in
commit 3b2d455.  Without this
directories specified directly as part of the rsnapshot::client config
don't work properly.

Author: Clayton O'Neill

templates/config.erb

@@ -101,5 +101,5 @@ exclude	<%= value %>
 ###############################
 
 <% @directories.each do |source_dir| -%>
-backup  <%= @client_user %>@<%= @name %>:<%= source_dir.gsub(/\/$/, '') %>/<%= "\t" %><%= "\t\t." %>
+backup	<%= @client_user %>@<%= @name %>:<%= source_dir.gsub(/\/$/, '') %>/<%= "\t" %><%= "\t\t." %>
 <% end -%>