升级composer

查看当前安装的版本 composer -v

C:\Users\A>composer
   ______
  / ____/___  ____ ___  ____  ____  ________  _____
 / /   / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__  )  __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
                    /_/
Composer version 1.9.0 2019-08-02 20:55:32

Usage:
  command [options] [arguments]

升级指令composer selfupdate

C:\Users\A>composer selfupdate
Updating to version 2.0.8 (stable channel).
   Downloading (100%)
Use composer self-update --rollback to return to version 1.9.0

还原上一个版本 composer self-update --rollback

C:\Users\A>composer self-update --rollback
Rolling back to version 2019-08-02_20-55-32-1.9.0.

升级composer到2.0.8之后，居然不支持tp5.1与tp6，被回滚到了1.9