修正：处理TCP连接的goroutine在退出前关闭连接

ebook/08.1.md

@@ -256,7 +256,7 @@ Go语言中通过net包中的`DialTCP`函数来建立一个TCP连接，并返回
 	func handleClient(conn net.Conn) {
 		conn.SetReadDeadline(time.Now().Add(2 * time.Minute)) // set 2 minutes timeout
 		request := make([]byte, 128) // set maxium request length to 128KB to prevent flood attack
-		
+		defer conn.Close()  // close connection before exit
 		for {
 			read_len, err := conn.Read(request)