Fix sh_crossbow ammo model (#446)

For some reason, the default model is set to shotgun shells when CrossbowRounds.mdl exists.

gamemode/items/ammo/sh_crossbowammo.txt

@@ -1,5 +1,5 @@
 ITEM.name = "Crossbow Bolts"
-ITEM.model = "models/Items/BoxBuckshot.mdl"
+ITEM.model = "models/Items/CrossbowRounds.mdl"
 ITEM.ammo = "XBowRounds" -- type of the ammo
 ITEM.ammoAmount = 5 -- amount of the ammo
 ITEM.description = "A Bundle of %s Crossbow Bolts"