Drop HHVM conflict (#10)

Author: keradus

composer.json

@@ -14,9 +14,6 @@
         "phpunit/phpunit": "^5.7.23 || ^6.4.3 || ^7.0 || ^8.0",
         "phpunitgoodpractices/polyfill": "^1.1"
     },
-    "conflict": {
-        "hhvm": "*"
-    },
     "require-dev": {
         "johnkary/phpunit-speedtrap": "^1.1 || ^2.0 || ^3.0",
         "symfony/phpunit-bridge": "^3.2.2 || ^4.0"