Centos7更改yum源

每次都要百度一番，还不如自己做个记录，简单粗暴，哈哈哈哈

cd /etc/yum.repos.d

mv CentOS-Base.repo CentOS-Base.repo.old

wget http://mirrors.aliyun.com/repo/Centos-7.repo

mv Centos-7.repo CentOS-Base.repo

yum clean all

yum makecache