Force PHPStan version

See phpstan/phpstan#1966

Author: Minishlink

composer.json

@@ -28,7 +28,7 @@
   },
   "require-dev": {
     "phpunit/phpunit": "^7.0",
-    "phpstan/phpstan": "^0.11",
+    "phpstan/phpstan": "0.11.2",
     "friendsofphp/php-cs-fixer": "^2.14"
   },
   "autoload": {