laravel , error not find in migrate:rollback

in laravel 5.1 , vagrant, when I run

php artisan migrate 

Migrated: 2017_04_20_205912_alter_3_discounts_table

but when I run

php artisan migrate:rollback

show this message :

[Symfony\Component\Debug\Exception\FatalThrowableError]
  Class 'Alter3DiscountsTable' not found

I Have this class but I don't know why show this message!

any body can help?

** I run composer dumpautoload and show this :

[RuntimeException]                                                                                                                                               
File at "/vendor/phpunit/php-code-coverage/src/CodeCoverage/Report/Node/Directory.php" does not exist, check your classmap definitions

via Chebli Mohamed