添加centos镜像地址

http://mirror.bit.edu.cn/centos/6.3/os/x86_64/
http://mirrors.163.com/centos/6.3/os/x86_64/
http://mirrors.neusoft.edu.cn/centos/6.3/os/x86_64/
http://mirror.neu.edu.cn/centos/6.3/os/x86_64/
http://mirrors.stuhome.net/centos/6.3/os/x86_64/
http://mirrors.btte.net/centos/6.3/os/x86_64/
http://mirrors.grandcloud.cn/centos/6.3/os/x86_64/
http://mirrors.ta139.com/centos/6.3/os/x86_64/
http://centos.ustc.edu.cn/centos/6.3/os/x86_64/
http://ftp.stu.edu.tw/Linux/CentOS/6.3/os/x86_64/
http://mirror01.idc.hinet.net/CentOS/6.3/os/x86_64/
http://ftp.cs.pu.edu.tw/Linux/CentOS/6.3/os/x86_64/
http://ftp.twaren.net/Linux/CentOS/6.3/os/x86_64/
http://ftp.nsysu.edu.tw/CentOS/6.3/os/x86_64/
http://ftp.stust.edu.tw/pub/Linux/CentOS/6.3/os/x86_64/
http://centos.tt.co.kr/6.3/os/x86_64/
http://data.nicehosting.co.kr/os/CentOS/6.3/os/x86_64/
http://centos.chlux.co.kr/6.3/os/x86_64/
http://ftp.daum.net/centos/6.3/os/x86_64/
http://mirror.yongbok.net/centos/6.3/os/x86_64/