Package error in sylius 1.8

[bigboss86]

After run composer install:

Problem 1
- phpunit/phpunit 8.5.0 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.1 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.2 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.3 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.4 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.5 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.6 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.7 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- phpunit/phpunit 8.5.8 requires sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2].
- Conclusion: don't install sebastian/diff 3.0.2
- Installation request for phpunit/phpunit ^8.5 -> satisfiable by phpunit/phpunit[8.5.0, 8.5.1, 8.5.2, 8.5.3, 8.5.4, 8.5.5, 8.5.6, 8.5.7, 8.5.8].