Mantis 匯出CSV檔變成亂碼

參考這篇進行修正
http://qq319319.pixnet.net/blog/post/37080242-%5B%E7%A8%8B%E5%BC%8F%E8%A8%AD%E8%A8%88%5Dmantis-bug-tracker%E5%8C%AF%E5%87%BAcsv%E6%AA%94%E4%BA%82%E7%A2%BC%E5%95%8F%E9%A1%8C