Fix NXDOMAIN detection

JeremyRand · JeremyRand · commit ca0fe5552806 · 2019-12-16T20:33:25.000Z
It was broken during the switch to modern btcd.
diff --git a/namecoin/namecoin.go b/namecoin/namecoin.go
@@ -1,7 +1,7 @@
 package namecoin
 
 import (
-	"github.com/namecoin/btcd/btcjson"
+	"github.com/btcsuite/btcd/btcjson"
 	"github.com/namecoin/btcd/rpcclient"
 	"gopkg.in/hlandau/madns.v2/merr"
 
