Bump PHPStan

Author: mbabker

composer.json

@@ -22,7 +22,7 @@
 	"require-dev": {
 		"cboden/ratchet": "^0.4.2",
 		"friendsofphp/php-cs-fixer": "^2.16.1",
-		"phpstan/phpstan": "^0.12.14",
+		"phpstan/phpstan": "^0.12.17",
 		"phpstan/phpstan-phpunit": "^0.12.6",
 		"phpunit/phpunit": "^8.5|^9.0"
 	},