Bump phpstan/phpstan from 0.12.80 to 0.12.81 in /dev-tools (#494)

Author: dependabot[bot]

dev-tools/composer.json

@@ -7,7 +7,7 @@
  "maglnet/composer-require-checker": "^3.1.0",
  "mi-schi/phpmd-extension": "^4.3.0",
  "phpmd/phpmd": "^2.9.1",
- "phpstan/phpstan": "^0.12.80",
+ "phpstan/phpstan": "^0.12.81",
  "phpstan/phpstan-strict-rules": "^0.12.9",
  "squizlabs/php_codesniffer": "^3.5.8",
  "vimeo/psalm": "^4.6.2"