Small fix for go < 1.1 versions
Small fix for go < 1.1 versions

hugozhu/dns,tsenart/dns,ezoic/dns,jdef/dns,skyportsystems/dns,asergeyev/dns,ErikDubbelboer/dns,skynet/dns,Git-Host/dns,ym/go-dns,AlexCheong/dns,cloudflare/dns,miekg/dns,michaelharo/dns,FiloSottile/dns,letsencrypt/dns,flebarbe/dns,Psiphon-Inc/dns,benbearchen/dns,josephyzhou/dns,janstk/dns,curtiszimmerman/dns,tonnerre/golang-dns,bragr/dns,rolandshoemaker/dns,tempbottle/dns,modulexcite/dns,jmhodges/dns,bboreham/dns