Fix native return typehint errors (#647)

Author: shmax

composer.json

@@ -18,7 +18,7 @@
     "doctrine/coding-standard": "^6.0",
     "phpbench/phpbench": "^0.14",
     "phpstan/extension-installer": "^1.0",
-    "phpstan/phpstan": "0.12.11",
+    "phpstan/phpstan": "0.12.18",
     "phpstan/phpstan-phpunit": "0.12.6",
     "phpstan/phpstan-strict-rules": "0.12.2",
     "phpunit/phpunit": "^7.2|^8.5",
@@ -54,7 +54,7 @@
     "lint" : "phpcs",
     "fix" : "phpcbf",
     "stan": "phpstan analyse --ansi --memory-limit 2048M",
-    "phpstan-baseline": "phpstan analyse --ansi --error-format baselineNeon > phpstan-baseline.neon",
+    "phpstan-baseline": "phpstan analyse --ansi --generate-baseline=phpstan-baseline.neon",
     "check": "composer lint && composer stan && composer test"
   }
 }