fix(golint): fix the warnings by go lint check. (#267)

diff --git a/core/api.go b/core/api.go
index a8941b6..79918f1 100644
--- a/core/api.go
+++ b/core/api.go
@@ -128,12 +128,13 @@
 	return newDefaultTransactionProducer(config, listener, arg)
 }
 
-// TransactionExecutor local executor for transaction message
+// TransactionLocalListener local listener for transaction message
 type TransactionLocalListener interface {
 	Execute(m *Message, arg interface{}) TransactionStatus
 	Check(m *MessageExt, arg interface{}) TransactionStatus
 }
 
+// TransactionProducer api for send transaction message
 type TransactionProducer interface {
 	baseAPI
 	// send a transaction message with sync
diff --git a/core/message.go b/core/message.go
index f6f4637..83db646 100644
--- a/core/message.go
+++ b/core/message.go
@@ -44,6 +44,8 @@
 	return fmt.Sprintf("[Topic: %s, Tags: %s, Keys: %s, Body: %s, DelayTimeLevel: %d, Property: %v]",
 		msg.Topic, msg.Tags, msg.Keys, msg.Body, msg.DelayTimeLevel, msg.Property)
 }
+
+//GetProperty get message property by key string
 func (msg *Message) GetProperty(key string) string {
 	ck := C.CString(key)
 	defer C.free(unsafe.Pointer(ck))
diff --git a/core/transaction_producer.go b/core/transaction_producer.go
index da57b33..09ae52f 100644
--- a/core/transaction_producer.go
+++ b/core/transaction_producer.go
@@ -45,8 +45,10 @@
 	"unsafe"
 )
 
+//TransactionStatus check the status if commit or rollback
 type TransactionStatus int
 
+//TransactionStatus check the status if commit or rollback
 const (
 	CommitTransaction   = TransactionStatus(C.E_COMMIT_TRANSACTION)
 	RollbackTransaction = TransactionStatus(C.E_ROLLBACK_TRANSACTION)
diff --git a/demos/transaction_producer.go b/demos/transaction_producer.go
index 8cf4112..762c4c8 100644
--- a/demos/transaction_producer.go
+++ b/demos/transaction_producer.go
@@ -41,18 +41,18 @@
 	sendTransactionMessage(pConfig)
 }
 
-type MyTransactionLocalListener struct {
+type myTransactionLocalListener struct {
 }
 
-func (l *MyTransactionLocalListener) Execute(m *rocketmq.Message, arg interface{}) rocketmq.TransactionStatus {
+func (l *myTransactionLocalListener) Execute(m *rocketmq.Message, arg interface{}) rocketmq.TransactionStatus {
 	return rocketmq.UnknownTransaction
 }
-func (l *MyTransactionLocalListener) Check(m *rocketmq.MessageExt, arg interface{}) rocketmq.TransactionStatus {
+func (l *myTransactionLocalListener) Check(m *rocketmq.MessageExt, arg interface{}) rocketmq.TransactionStatus {
 	return rocketmq.CommitTransaction
 }
 func sendTransactionMessage(config *rocketmq.ProducerConfig) {
-	listener := &MyTransactionLocalListener{}
-	producer, err := rocketmq.NewTransactionProducer(config, listener, listener)
+	listener := &myTransactionLocalListener{}
+	producer, err := rocketmq.NewTransactionProducer(config, listener, nil)
 
 	if err != nil {
 		fmt.Println("create Transaction producer failed, error:", err)
@@ -69,7 +69,7 @@
 	fmt.Printf("Transaction producer: %s started... \n", producer)
 	for i := 0; i < 10; i++ {
 		msg := fmt.Sprintf("%s-%d", "Hello,Transaction MQ Message-", i)
-		result, err := producer.SendMessageTransaction(&rocketmq.Message{Topic: "YourTopicXXXXXXXX", Body: msg}, msg)
+		result, err := producer.SendMessageTransaction(&rocketmq.Message{Topic: "YourTopicXXXXXXXX", Body: msg}, nil)
 		if err != nil {
 			fmt.Println("Error:", err)
 		}