尝试通过composer安装Laravel时出现以下错误，可能是什么问题？
操作系统：Ubuntu
php：5.6
apache：2.4
错误
PHP Fatal error: Interface 'Psr\Log\LoggerInterface' not found in /var/www/html/hak/vendor/laravel/framework/src/Illuminate/Log/Writer.php on line 21
Script php artisan clear-compiled handling the post-install-cmd event returned with an error