Update rector/rector requirement from ^1.2.0 to ^1.2.1 (#648)

Updates the requirements on [rector/rector](https://github.com/rectorphp/rector) to permit the latest version.
- [Release notes](https://github.com/rectorphp/rector/releases)
- [Commits](rectorphp/rector@1.2.0...1.2.1)

---
updated-dependencies:
- dependency-name: rector/rector
  dependency-type: direct:development
...

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composer.json

@@ -33,7 +33,7 @@
         "phpstan/phpstan": "^1.11.7",
         "phpstan/phpstan-phpunit": "^1.4.0",
         "phpunit/phpunit": "^8.5.38",
-        "rector/rector": "^1.2.0"
+        "rector/rector": "^1.2.1"
     },
     "suggest": {
         "ext-mbstring": "for parsing UTF-8 CSS"