报错信息：
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.
Problem 1
- doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.22) does not satisfy that requirement.
- doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.22) does not satisfy that requirement.
- Installation request for doctrine/instantiator 1.1.0 -> satisfiable by doctrine/instantiator[1.1.0].
解决方法：
删除 composer.lock 文件，重新执行 composer install，这样就能重新生成 composer.lock 文件了