ABR-40 minor grammar fix (#7593)

# About the pull request
Corrects the grammar of the ABR-40 rifle's description by removing a
second period at the end of it's sentence.
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# Explain why it's good for the game
Corrects grammatical error. 
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
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</details>


# Changelog
:cl:
del: A single period from the ABR-40 description that shouldn't be
there.
/:cl:

code/modules/projectiles/guns/rifles.dm

@@ -1664,7 +1664,7 @@
 
 /obj/item/weapon/gun/rifle/l42a/abr40
 	name = "\improper ABR-40 hunting rifle"
-	desc = "The civilian version of the L42A battle rifle. Almost identical and even cross-compatible with L42 magazines, just don't take the stock off.."
+	desc = "The civilian version of the L42A battle rifle. Almost identical and even cross-compatible with L42 magazines, just don't take the stock off."
 	desc_lore = "The ABR-40 was created along-side the L42A as a hunting rifle for civilians. Sporting faux wooden furniture and a legally-mandated 12 round magazine, it's still highly accurate and deadly, a favored pick of experienced hunters and retired Marines. However, it's very limited in attachment selection, only being able to fit rail attachments, and the differences in design from the L42 force an awkward pose when attempting to hold it one-handed. Removing the stock is not recommended."
 	icon = 'icons/obj/items/weapons/guns/guns_by_faction/colony.dmi'
 	icon_state = "abr40"