fix golint issues in core/queue (#507)

core/queue/multipusher.go

@@ -2,11 +2,13 @@ package queue
 
 import "github.com/tal-tech/go-zero/core/errorx"
 
+// A MultiPusher is a pusher that can push messages to multiple underlying pushers.
 type MultiPusher struct {
 	name    string
 	pushers []Pusher
 }
 
+// NewMultiPusher returns a MultiPusher.
 func NewMultiPusher(pushers []Pusher) Pusher {
 	return &MultiPusher{
 		name:    generateName(pushers),
@@ -14,10 +16,12 @@ func NewMultiPusher(pushers []Pusher) Pusher {
 	}
 }
 
+// Name returns the name of pusher.
 func (pusher *MultiPusher) Name() string {
 	return pusher.name
 }
 
+// Push pushes a message into the underlying queue.
 func (pusher *MultiPusher) Push(message string) error {
 	var batchError errorx.BatchError