Bump PHPUnit minimum versions

Author: carusogabriel

composer.json

@@ -21,7 +21,7 @@
     "require-dev": {
         "symfony/serializer":           "^2.7|^3.0|^4.0",
         "symfony/debug":                "^2.7|^3.0|^4.0",
-        "phpunit/phpunit":              "^4.8|^5.0"
+        "phpunit/phpunit":              "^4.8.35|^5.4.3"
     },
     "replace": {
         "oldsound/rabbitmq-bundle": "self.version"