fix for latest micro

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

message.go

@@ -2,24 +2,28 @@ package http
 
 import (
 	"go.unistack.org/micro/v3/client"
+	"go.unistack.org/micro/v3/metadata"
 )
 
 type httpMessage struct {
 	payload     interface{}
 	topic       string
 	contentType string
+	opts        client.MessageOptions
 }
 
 func newHTTPMessage(topic string, payload interface{}, contentType string, opts ...client.MessageOption) client.Message {
 	options := client.NewMessageOptions(opts...)
-	if len(options.ContentType) == 0 {
-		options.ContentType = contentType
+
+	if len(options.ContentType) > 0 {
+		contentType = options.ContentType
 	}
 
 	return &httpMessage{
 		payload:     payload,
 		topic:       topic,
-		contentType: options.ContentType,
+		contentType: contentType,
+		opts:        options,
 	}
 }
 
@@ -34,3 +38,7 @@ func (h *httpMessage) Topic() string {
 func (h *httpMessage) Payload() interface{} {
 	return h.payload
 }
+
+func (h *httpMessage) Metadata() metadata.Metadata {
+	return h.opts.Metadata
+}