我尝试添加 ppa 以安装 Ubuntu Tweak，但我不能这样做。终端打印：无法添加 PPA：'ppa:tualatrix/ppa'。请检查 PPA 名称或格式是否正确。那么如何安装 Ubuntu Tweak？
>uname -a
Linux Inspiron-15-3552 3.13.0-161-generic #211-Ubuntu
SMP Wed Oct 3 14:52:35 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
>lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 14.04.5 LTS
Release: 14.04
Codename: trusty
>sudo add-apt-repository ppa:tualatrix/ppa
Cannot add PPA: 'ppa:tualatrix/ppa'.
Please check that the PPA name or format is correct.