Update phpunit/phpunit requirement from 4.* to 4.* || 5.*

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/5.7.27/ChangeLog-5.7.md)
- [Commits](sebastianbergmann/phpunit@4.0.0...5.7.27)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

composer.json

@@ -20,7 +20,7 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "2.*",
-        "phpunit/phpunit": "4.*",
+        "phpunit/phpunit": "4.* || 5.*",
         "squizlabs/php_codesniffer": "3.*"
     },
     "autoload": {