PHP artisan migrate:refresh --seed 报错

报如下错，这是什么原因？

vagrant@homestead:~/Code/larabbs$ php artisan migrate:refresh --seed
PHP Fatal error:  Uncaught Error: Class 'Composer\Autoload\ComposerStaticInitcf99d8565b35db0a1fb45e20887e7f96' not found in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php:30
Stack trace:
#0 /home/vagrant/Code/larabbs/vendor/autoload.php(7): ComposerAutoloaderInitcf99d8565b35db0a1fb45e20887e7f96::getLoader()
#1 /home/vagrant/Code/larabbs/artisan(18): require('/home/vagrant/C...')
#2 {main}
  thrown in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php on line 30

Fatal error: Uncaught Error: Class 'Composer\Autoload\ComposerStaticInitcf99d8565b35db0a1fb45e20887e7f96' not found in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php:30
Stack trace:
#0 /home/vagrant/Code/larabbs/vendor/autoload.php(7): ComposerAutoloaderInitcf99d8565b35db0a1fb45e20887e7f96::getLoader()
#1 /home/vagrant/Code/larabbs/artisan(18): require('/home/vagrant/C...')
#2 {main}
  thrown in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php on line 30
vagrant@homestead:~/Code/larabbs$ php artisan migrate:refresh --seed
PHP Fatal error:  Uncaught Error: Class 'Composer\Autoload\ComposerStaticInitcf99d8565b35db0a1fb45e20887e7f96' not found in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php:30
Stack trace:
#0 /home/vagrant/Code/larabbs/vendor/autoload.php(7): ComposerAutoloaderInitcf99d8565b35db0a1fb45e20887e7f96::getLoader()
#1 /home/vagrant/Code/larabbs/artisan(18): require('/home/vagrant/C...')
#2 {main}
  thrown in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php on line 30

Fatal error: Uncaught Error: Class 'Composer\Autoload\ComposerStaticInitcf99d8565b35db0a1fb45e20887e7f96' not found in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php:30
Stack trace:
#0 /home/vagrant/Code/larabbs/vendor/autoload.php(7): ComposerAutoloaderInitcf99d8565b35db0a1fb45e20887e7f96::getLoader()
#1 /home/vagrant/Code/larabbs/artisan(18): require('/home/vagrant/C...')
#2 {main}
  thrown in /home/vagrant/Code/larabbs/vendor/composer/autoload_real.php on line 30