我正在使用 Ubuntu 16.04 LTS amd64。我已经安装了 LAMP（php5.6、apache2、mysql）和 Composer。我从github下载了我的laravel项目。我想更新 Composer 以启动本地服务器php artisan serve。但是当我想运行时localhost，终端说：
heartprogrammer@heartprogrammer-desktop:/var/www/kstu$ php artisan serve
PHP Warning: require(/var/www/kstu/bootstrap/../vendor/autoload.php): failed to open stream: No such file or directory in /var/www/kstu/bootstrap/autoload.php on line 17
PHP Fatal error: require(): Failed opening required '/var/www/kstu/bootstrap/../vendor/autoload.php' (include_path='.:/usr/share/php') in /var/www/kstu/bootstrap/autoload.php on line 17
我尝试更新 Composer，但它说：
heartprogrammer@heartprogrammer-desktop:/var/www/kstu$ composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
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