UMG-40 heavy barrel attachment has wrong description

The UMG-40 SMG's heavy barrel attachment incorrectly has the same description as the extended barrel, except "extended" was changed to "heavy": "Heavy barrel that increases projectile velocity and enables a faster transition to aim down sights (ADS)." Fortunately, the stats appear consistent with heavy barrel attachments on other weapons.

On other weapons, the heavy barrel attachment's description is typically "Heavy barrel that improves firing accuracy over extended periods."