D:phpstudy_proWWW>composer selfupdate
Updating to version 2.0.8 (stable channel).
Downloading (100%)
Failed to decode response: zlib_decode(): data error
Retrying with degraded mode, check https://getcomposer.org/doc/a... for more info
起因：网络问题。
解决办法**
composer页提供了一个degraded模式的解决办法。如果咱们开启了ipv6则须要将IPv6勾销勾选。