Fix permission checking in MediaAdminController::show()
Fix permission checking in MediaAdminController::show()

The `SHOW` permission does no exist. The correct permission is `VIEW` (and is correctly used in `SonataAdminBundle`).
vyshkant/SonataMediaBundle,nicolasricci/SonataMediaBundle,bgaleotti/SonataMediaBundle,hug963/SonataMediaBundle,jerome-fix/SonataMediaBundle,sonata-project/SonataMediaBundle,nicolasricci/SonataMediaBundle,OskarStark/SonataMediaBundle,OskarStark/SonataMediaBundle,hug963/SonataMediaBundle,bgaleotti/SonataMediaBundle,jerome-fix/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,bgaleotti/SonataMediaBundle,rmzamora/SonataMediaBundle,nicolasricci/SonataMediaBundle,vyshkant/SonataMediaBundle,vyshkant/SonataMediaBundle,jerome-fix/SonataMediaBundle,bgaleotti/SonataMediaBundle,vyshkant/SonataMediaBundle,jerome-fix/SonataMediaBundle,hug963/SonataMediaBundle,nicolasricci/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,OskarStark/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,rmzamora/SonataMediaBundle,hug963/SonataMediaBundle,OskarStark/SonataMediaBundle,nicolasricci/SonataMediaBundle,rmzamora/SonataMediaBundle,hug963/SonataMediaBundle,vyshkant/SonataMediaBundle,Soullivaneuh/SonataMediaBundle