Fix dependencies

Author: Lander Vanderstraeten

composer.json

@@ -4,9 +4,9 @@
     "type": "library",
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.12",
-        "phpro/grumphp": "^0.14.1",
-        "phpspec/phpspec": "^4.3",
-        "symfony/validator": "^4.1",
+        "phpro/grumphp": "^0.17",
+        "phpspec/phpspec": "^6.0",
+        "symfony/validator": "^4.4",
         "sebastian/comparator": "^1.2.4"
     },
     "license": "MIT",