fixed one concurrency problem in admin.Close() detected when running the

tests 100 times.

Makefile

@@ -14,7 +14,7 @@ vet: fmt
 	go vet ./...
 
 test: build
-	go test -v -count=1 ./...
+	go test -count=1 ./...
 
 build: generate vet
 	mkdir -p bin

pkg/server/admin/admin.go

@@ -87,6 +87,9 @@ func NewAdmin() *Admin {
 }
 
 func (admin *Admin) Close() {
+	admin.mutex.Lock()
+	defer admin.mutex.Unlock()
+
 	for _, client := range admin.clients {
 		client.clientConnection.Close()
 		client.agentConnection.Close()