[Bridge/PhpUnit] dont conflict with phpunit 4.8

Author: nicolas-grekas

composer.json

@@ -24,7 +24,7 @@
         "symfony/error-handler": "For tracking deprecated interfaces usages at runtime with DebugClassLoader"
     },
     "conflict": {
-        "phpunit/phpunit": "<5.4.3"
+        "phpunit/phpunit": "<4.8.35|<5.4.3,>=5.0"
     },
     "autoload": {
         "files": [ "bootstrap.php" ],