补充：执行 yum install php-xml，安装DOM扩展，

最后报错：php版本冲突：

Error: php56w-common conflicts with php-common-5.4.16-45.el7.x86_64
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest

不知道该怎么办？