Add PHPUnit 7.0 conflict

Author: Slamdunk

composer.json

@@ -9,7 +9,7 @@
         "php": "^7.0"
     },
     "conflict": {
-        "phpunit/phpunit": "<6.0"
+        "phpunit/phpunit": "<6.0 || >6.5"
     },
     "require-dev": {
         "phpunit/phpunit": "^6.0"