Granularizes riot shields similarly to armor and guns. (shiptest-ss13…

…#2961)

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## About The Pull Request
as it says! 600 credits for one riot shield

## Why It's Good For The Game

good for similar reasons the other ones were you dont get more riot
shields than you ened and people might use them more this way :)
## Changelog

:cl:

tweak: Riot shield crates now contain only one shield but are priced at
600 credits.
/:cl:

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code/modules/cargo/packs/sec_supply.dm

@@ -56,11 +56,9 @@
 
 /datum/supply_pack/sec_supply/riotshields
 	name = "Riot Shields Crate"
-	desc = "For when the greytide gets really uppity. Contains three riot shields."
-	cost = 2000
-	contains = list(/obj/item/shield/riot,
-					/obj/item/shield/riot,
-					/obj/item/shield/riot)
+	desc = "Contains a riot shield, effective at holding back hostile fauna, xenofauna, or large crowds."
+	cost = 600
+	contains = list(/obj/item/shield/riot)
 	crate_name = "riot shields crate"
 
 /datum/supply_pack/sec_supply/survknives