composer(deps-dev): bump phpstan/phpstan from 1.5.3 to 1.5.4

Bumps [phpstan/phpstan](https://github.com/phpstan/phpstan) from 1.5.3 to 1.5.4.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/1.6.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.5.3...1.5.4)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -22,7 +22,7 @@
     "ergebnis/composer-normalize": "^2.20.0",
     "ergebnis/license": "^1.1.0",
     "phpstan/extension-installer": "^1.1.0",
-    "phpstan/phpstan": "^1.5.3",
+    "phpstan/phpstan": "^1.5.4",
     "phpstan/phpstan-deprecation-rules": "^1.0.0",
     "phpstan/phpstan-phpunit": "^1.1.0",
     "phpstan/phpstan-strict-rules": "^1.1.0",