Restrict compatible PHP versions to currently supported ones. We haven't tested PHP 7.4 and 8.0 yet. (#858)

Author: YetiCGN

composer.json

@@ -11,7 +11,7 @@
         }
     ],
     "require": {
-        "php": ">=5.6",
+        "php": ">=5.6,<7.3",
         "symfony/framework-bundle": "^2.8|^3.0|^4",
         "symfony/console": "^2.8|^3.0|^4",
         "symfony/stopwatch": "^2.8|^3.0|^4",