scripts: lhosts: backup the last hosts file
scripts: lhosts: backup the last hosts file

备份上一次的 hosts 文件至 /etc/hosts.bak

同时用 cat 指令替换 mv，防止出现以下情况：

    $ sudo mv hosts /etc/

输出错误信息：

mv: cannot move ‘hosts’ to ‘/etc/hosts’: Device or resource busy

ruidalin/hosts,VegetaPn/hosts,Xiejiayun/hosts,Xiejiayun/hosts,racaljk/hosts,Xiejiayun/hosts,wsdjeg/hosts,coolrc136/hosts