Update phpstan/phpstan requirement from 0.12.85 to 0.12.87 (#106)

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Commits](phpstan/phpstan@0.12.85...0.12.87)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

composer.json

@@ -15,7 +15,7 @@
 		"pocketmine/snooze": "^0.1.0"
 	},
 	"require-dev": {
-		"phpstan/phpstan": "0.12.85",
+		"phpstan/phpstan": "0.12.87",
 		"phpstan/phpstan-strict-rules": "^0.12.2"
 	},
 	"autoload": {