Composer: update CS dependencies

WordPressCS 3.0.0 (and 3.0.1) has been released.

This commit updates the Composer dependencies to use the new version, including updating the underlying PHP_CodeSniffer dependency to the new minimum supported version for WPCS.

Note: the Composer PHPCS installer plugin is no longer explicitly required as it is now a dependency of WordPressCS, so we inherit the dependency automatically.

composer.json

@@ -17,7 +17,7 @@
 	},
 	"require-dev": {
 		"squizlabs/php_codesniffer": "3.7.2",
-		"wp-coding-standards/wpcs": "~3.0.0",
+		"wp-coding-standards/wpcs": "~3.0.1",
 		"phpcompatibility/phpcompatibility-wp": "~2.1.3",
 		"yoast/phpunit-polyfills": "^1.1.0"
 	},