Fix phpstan dependency

Author: alterphp

composer.json

@@ -36,7 +36,7 @@
         "doctrine/doctrine-fixtures-bundle": "^3.0",
         "friendsofphp/php-cs-fixer": "^2.11",
         "php-coveralls/php-coveralls": "^2.0",
-        "phpstan/phpstan": "dev-master",
+        "phpstan/phpstan": "^0.12",
         "psr/log": "~1.0",
         "symfony/browser-kit": "^4.2|^5.0",
         "symfony/console": "^4.2|^5.0",