Use @IsGranted annotation instead of @Security

[voronkovich]

Recently a new @IsGranted annotation was introduced. It's just a shortcut for the well-known @Security annotation. See: https://github.com/sensiolabs/SensioFrameworkExtraBundle/blob/master/Configuration/IsGranted.php

[javiereguiluz]

I think this could be a good idea to show the new annotation in action.

[javiereguiluz]

Fixed by #797.