composer update 的时候出现：
[Composer\Downloader\TransportException]
The "https://packagist.org/p/provider-2018-10%24ceed846c1a187d8670540d62ead2c32137653431a06bf2c84d5fb2e04ed484b5.json" file could not be downloaded (HTTP/1.1 404 Not Found)
解决方法：
执行composer clear-cache
