cleanups: go vet/golint (#331)

Go vet and golint the new code once again.

Drop Name from NameTemplate - it's cleaner: nametemplate.Template.

middleware/proxy/proxy.go

@@ -17,7 +17,7 @@ var errUnreachable = errors.New("unreachable backend")
 // Proxy represents a middleware instance that can proxy requests to another DNS server.
 type Proxy struct {
 	Next      middleware.Handler
-	Client    *Client
+	Client    *client
 	Upstreams []Upstream
 }