A small nerf to the "Creature" spawn (#20678)

This change reduces the damage that the green, watermelon-looking
"Creature" mobs are capable of.

Previously, their attacks had a damage range of 20-50. For comparison,
Plains Tyrant and Cavern Geist do 40 damage an attack.

The Xenoarchaology item that spawns these green dudes seems to be
capable of spawning them pretty quickly - and when you're fighting
simple mobs that are able to break your bones and give you an arterial
bleed in a single hit, that gets silly pretty fast.

I've tweaked the damage numbers so that the Creatures are a little
stronger than Hivebot Guardians in terms of damage.

code/modules/mob/living/simple_animal/hostile/creature.dm

@@ -7,8 +7,8 @@
 	icon_dead = "otherthing-dead"
 	health = 80
 	maxHealth = 80
-	melee_damage_lower = 25
-	melee_damage_upper = 50
+	melee_damage_lower = 20
+	melee_damage_upper = 30
 	organ_names = list("meaty core")
 	attacktext = "chomped"
 	attack_sound = 'sound/weapons/bite.ogg'