minor #1059 Make tests compatible with PHPUnit 8 (voronkovich)

This PR was merged into the master branch.

Discussion
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Make tests compatible with PHPUnit 8

`setUp()` method must have a `void` return type declaration. See: https://phpunit.de/announcements/phpunit-8.html

Commits
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dae754d Make tests compatible with PHPUnit 8

Author: javiereguiluz

tests/Command/AddUserCommandTest.php

@@ -26,7 +26,7 @@ class AddUserCommandTest extends KernelTestCase
         'full-name' => 'Chuck Norris',
     ];
 
-    protected function setUp()
+    protected function setUp(): void
     {
         exec('stty 2>&1', $output, $exitcode);
         $isSttySupported = 0 === $exitcode;