You could try using --skip-broken to work around the problem

cd /etc/yum.repos.d

cd ..

mkdir repoBack

cd /etc/yum.repos.d

mv * ../repoBack

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

mv Centos-7.repo CentOS-Base.repo

yum clean all

yum makecache

yum update