BUGFIX: couldn't upload backup on OSX

--B is not a valid df option on OSX

app/controllers/admin/backups_controller.rb

@@ -135,7 +135,7 @@ class Admin::BackupsController < Admin::AdminController
   private
 
   def has_enough_space_on_disk?(size)
-    `df -l -B 1K . | tail -1 | tr -s ' ' | cut -d ' ' -f 4`.to_i > size / 1024
+    `df -Pk . | awk 'NR==2 {print $4 * 1024;}'`.to_i > size
   end
 
 end