[PHPStan] Update to PHPStan ^1.6

Author: samsonasik

composer.json

@@ -71,7 +71,7 @@
         "mezzio/mezzio-laminasviewrenderer": "^2.3",
         "northwoods/container": "^3.0",
         "php-coveralls/php-coveralls": "^2.4",
-        "phpstan/phpstan": "1.5.6 as 1.6",
+        "phpstan/phpstan": "^1.6.7",
         "phpstan/phpstan-webmozart-assert": "^1.0",
         "pimple/pimple": "^3.2",
         "rector/rector": "dev-main",