[fix] Router adds extra period in generated route names

When creating a resource controller with a name prefix (via the `as` option), an extra period is sometimes added to the route names (e.g., `bar..foo.create` instead of `bar.foo.create`).

```php
// Should generate named routes 'bar.foo.index', 'bar.foo.create', etc.
// but it gives 'bar..foo.index', etc. instead.
$router->resource('foo', 'FooController', [
    'as' => 'bar'
]);
```

This PR simply removes a period from the `getGroupResourceName()` method because one is already added in `getResourceName()`.