composer错误_Content-Length mismatch, received 84697 bytes out of the expected..

使用composer下载源码出现错误 

[Composer\Downloader\TransportException]                               

composer config repo.packagist composer https://packagist.phpcomposer.com

解决办法：更换源，改到国内来 

composer config repo.packagist composer https://packagist.phpcomposer.com