Fixed canonical redirects on non-root url app instances

Fixed canonical redirects on non-root url app instances

If BookStack instance is deployed to any non-root path, e.g. http://example.com/wiki/,
requests for http://example.com/wiki/shelves/
was redirected to http://example.com/shelves
instead of http://example.com/wiki/shelves

Synced with: https://github.com/laravel/laravel/blob/master/public/.htaccess