Start a new routine when subscribing (#2297)

diff --git a/registry/protocol/protocol.go b/registry/protocol/protocol.go
index cbc610a..822f622 100644
--- a/registry/protocol/protocol.go
+++ b/registry/protocol/protocol.go
@@ -161,7 +161,7 @@
 		logger.Errorf("Directory %v is expected to implement Directory, and will return nil invoker!", dic)
 		return nil
 	}
-	regDic.Subscribe(registryUrl.SubURL)
+	go regDic.Subscribe(registryUrl.SubURL)
 
 	err = reg.Register(serviceUrl)
 	if err != nil {