Fix signing
Fix signing

Fix the signing - the memory usage of the Zone structure is bad - and
needs to be fixed somehow.

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