Centos 7 updates yum source to Alibaba Cloud

yum install wget -y
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
cd /etc/yum.repos.d/
wget http://mirrors.aliyun.com/repo/Centos-7.repo
mv Centos-7.repo CentOS-Base.repo
yum makecache
yum -y update