dns.resolveSoa(hostname, callback)
- 
hostname<string> - 
callback<Function> 
使用域名系统协议来解析 hostname 的起始规范记录(SOA 记录)。传给 callback 函数的 address 参数将是具有以下属性的对象:
¥Uses the DNS protocol to resolve a start of authority record (SOA record) for
the hostname. The address argument passed to the callback function will
be an object with the following properties:
- 
nsname - 
hostmaster - 
serial - 
refresh - 
retry - 
expire - 
minttl 
{
  nsname: 'ns.example.com',
  hostmaster: 'root.example.com',
  serial: 2013101809,
  refresh: 10000,
  retry: 2400,
  expire: 604800,
  minttl: 3600
}