Suppress file_get_contents error in the admin dashboard

I have here `allow_url_fopen` disabled, and as this is a considerable security issue, it's so on a number of webhosting solutions.    
What I propose is just to insert a @ character before `file_get_contents` in /vendor/traq/controllers/admin/dashboard.php. Those devs who have this disabled will have to update manually, but they won't get annoying error messages. They are especially annoying when better_php_errors is installed for debugging.