Composer: allow for the 1.0.0 version of the Composer PHPCS plugin

The Composer PHPCS plugin has released its 1.0.0 version. 🎉

Important:
I've _widened_ the version constraints for the plugin, instead of _bumping_ it.

The reason for this is to prevent conflicts with end-user projects/other external PHPCS standards which may also require(-dev) the plugin, but may not (yet) have updated _their_ constraints for the plugin.
If the version would have been bumped instead of widened, those users would get an unsolvable conflict during the `composer install` run (unless they `require-dev` the plugin for the root project, but then, that's exactly what we _don't_ want them to do as external standards managing the versions of the plugins should  be more reliable).

Ref: https://github.com/PHPCSStandards/composer-installer/releases/tag/v1.0.0

Author: jrfnl

composer.json

@@ -14,7 +14,7 @@
         "jakub-onderka/php-code-style": "*"
     },
     "require": {
-        "dealerdirect/phpcodesniffer-composer-installer": "^0.7",
+        "dealerdirect/phpcodesniffer-composer-installer": "^0.7 || ^1.0",
         "phpcompatibility/php-compatibility": "^9.3",
         "squizlabs/php_codesniffer": "^3.6.1"
     },