Update composer.json

Author: patrickbrouwers

composer.json

@@ -25,7 +25,7 @@
     "laravel-doctrine/orm": "^1.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "^6.0",
+    "phpunit/phpunit": "^4.0",
     "mockery/mockery": "~0.9"
   },
   "autoload": {