Convert between the API implictily absolute and DO standard record names

Previously, this DNS provider incorrectly assumed that DNS records
passed to it followed the standard notation, used by the DigitalOcean
API, that absolute DNS record names end with a dot, and relative DNS
record names don't.

This is incorrect because libdns uses de-facto implicitly absolute DNS
record names with a dot suffix, which causes any DNS record added with
eg certmagic to incorrectly be treated as relative, resulting in records
like: _acme-challenge.example.org.example.org

This fixes this issue by converting between the standard dot-suffix DNS
record name notation used by the DigitalOcean API and the implicitly
absolute record names used by libdns.

See: libdns/libdns#12

client.go

@@ -3,6 +3,7 @@ package digitalocean
 import (
 	"context"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -39,7 +40,7 @@ func (p *Provider) getDNSEntries(ctx context.Context, zone string) ([]libdns.Rec
 
 		for _, entry := range domains {
 			record := libdns.Record{
-				Name:  entry.Name,
+				Name:  entry.Name + "." + strings.Trim(zone, ".") + ".",
 				Value: entry.Data,
 				Type:  entry.Type,
 				TTL:   time.Duration(entry.TTL) * time.Second,
@@ -72,7 +73,7 @@ func (p *Provider) addDNSEntry(ctx context.Context, zone string, record libdns.R
 	p.getClient()
 
 	entry := godo.DomainRecordEditRequest{
-		Name: record.Name,
+		Name: strings.Trim(strings.ReplaceAll(record.Name, zone, ""), "."),
 		Data: record.Value,
 		Type: record.Type,
 		TTL:  int(record.TTL.Seconds()),
@@ -118,7 +119,7 @@ func (p *Provider) updateDNSEntry(ctx context.Context, zone string, record libdn
 	}
 
 	entry := godo.DomainRecordEditRequest{
-		Name: record.Name,
+		Name: strings.Trim(strings.ReplaceAll(record.Name, zone, ""), "."),
 		Data: record.Value,
 		Type: record.Type,
 		TTL:  int(record.TTL.Seconds()),