update http header

request.go

@@ -23,6 +23,8 @@ const (
 	// ReqContentTypeMultipart multipart/form-data
 	ReqContentTypeMultipart = `multipart/form-data`
 
+	// HTTP header Accept
+	Accept = `Accept`
 	// HTTP header Accept-Encoding
 	AcceptEncoding = `Accept-Encoding`
 	// HTTP header Content-Type