centos6升级php时误安装：
rpm -Uvh https://mirror.webtatic.com/yum/el7/epel-release.rpm
rpm -Uvh https://mirror.webtatic.com/yum/el7/webtatic-release.rpm
导致：Error: xz compression not available
解决办法记录如下：
[root@web-1 epel]# yum remove epel-release
[root@web-1 epel]# rm -rf /var/cache/yum/x86_64/6/epel/*
[root@web-1 epel]# rpm -Uvh http://mirror.webtatic.com/yum/el6/latest.rpm