为什么在linux上面使用composer安装 leon2012/snowflake 会出现找不到类的错误？

Question

注：在windows上面是可以的

<?php
require_once '/home/wangn/ws/php/me/vendor/autoload.php';

$a = new Leon2012\Snowflake\Snowflake(1);
$b = $a->next();
var_dump($b);

php ./test/a.php 
PHP Fatal error:  Uncaught Error: Class 'Leon2012\Snowflake\Snowflake' not found in /home/wangn/ws/php/me/test/a.php:5
Stack trace:
#0 {main}
  thrown in /home/wangn/ws/php/me/test/a.php on line 5