minor #2755 Fix compatibility with PHPUnit 5.4.x (keradus)

This PR was merged into the 2.2 branch.

Discussion
----------

Fix compatibility with PHPUnit 5.4.x

Commits
-------

860be69e Fix compatibility with PHPUnit 5.4.x

composer.json

@@ -34,7 +34,7 @@
         "gecko-packages/gecko-php-unit": "^2.0",
         "johnkary/phpunit-speedtrap": "^1.0.1",
         "justinrainbow/json-schema": "^5.0",
-        "phpunit/phpunit": "^4.8.35 || ^5.4",
+        "phpunit/phpunit": "^4.8.35 || ^5.4.3",
         "satooshi/php-coveralls": "^1.0",
         "symfony/phpunit-bridge": "^3.2.2"
     },