Update friendsofphp/php-cs-fixer requirement from 2.16.3 to 2.16.4 (#74)

Updates the requirements on [friendsofphp/php-cs-fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) to permit the latest version.
- [Release notes](https://github.com/FriendsOfPHP/PHP-CS-Fixer/releases)
- [Changelog](https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/2.16/CHANGELOG.md)
- [Commits](PHP-CS-Fixer/PHP-CS-Fixer@v2.16.3...v2.16.4)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

composer.json

@@ -34,7 +34,7 @@
     },
     "require-dev": {
         "phpunit/php-code-coverage": "^4.0 || ^5.0 || ^6.0 || ^7.0",
-        "friendsofphp/php-cs-fixer": "2.16.3",
+        "friendsofphp/php-cs-fixer": "2.16.4",
         "phpstan/phpstan": "0.12.19",
         "vimeo/psalm": "3.11.4"
     },