Fix logout redirect

Updated property logoutRedirect to alias "@web" …

The use of the value "/" caused a 404 Error, under certain settings of the urlManager / pretty URLs.
```php
...
		'urlManager' => [
			'enablePrettyUrl' => true,
			//'enableStrictParsing' => true,
			'showScriptName' => false,
			'suffix' => '/',
			'rules' => [
				//custom site controller rules
                '' => 'site/index',
                '<_a:(about|contact|error|captcha)>' => 'site/<_a>',
...
```