Update suggested version of Composer PHPCS plugin

The DealerDirect Composer plugin has just released version `0.6.0`.
As Composer treats minors < 1.0 as majors, updating to this version requires an update to the `composer.json` requirements.

> For pre-1.0 versions it also acts with safety in mind and treats ^0.3 as >=0.3.0 <0.4.0.

Refs:
* https://github.com/Dealerdirect/phpcodesniffer-composer-installer/releases/tag/v0.6.0
* https://getcomposer.org/doc/articles/versions.md#caret-version-range-

Author: jrfnl

README.md

@@ -32,7 +32,7 @@ The only supported installation method is via [Composer](https://getcomposer.org
 
 If you don't have a Composer plugin installed to manage the `installed_paths` setting for PHP_CodeSniffer, run the following from the command-line:
 ```bash
-composer require --dev dealerdirect/phpcodesniffer-composer-installer:^0.5.0 phpcompatibility/phpcompatibility-passwordcompat:*
+composer require --dev dealerdirect/phpcodesniffer-composer-installer:^0.6 phpcompatibility/phpcompatibility-passwordcompat:*
 composer install
 ```
 

composer.json

@@ -21,11 +21,11 @@
     "phpcompatibility/php-compatibility" : "^9.0"
   },
   "require-dev" : {
-    "dealerdirect/phpcodesniffer-composer-installer": "^0.5",
+    "dealerdirect/phpcodesniffer-composer-installer": "^0.6",
     "ircmaxell/password-compat": "dev-master"
   },
   "suggest" : {
-    "dealerdirect/phpcodesniffer-composer-installer": "^0.5 || This Composer plugin will sort out the PHP_CodeSniffer 'installed_paths' automatically.",
+    "dealerdirect/phpcodesniffer-composer-installer": "^0.6 || This Composer plugin will sort out the PHP_CodeSniffer 'installed_paths' automatically.",
     "roave/security-advisories": "dev-master || Helps prevent installing dependencies with known security issues."
   },
   "prefer-stable" : true