Switch the bats undead variation to 'saurian'

(default doesn't make sense here, and IMHO among the available ones
'saurian' fits better)

changelog

@@ -10,6 +10,9 @@ Version 1.3.8+svn:
   * Son of the Black Eye
     * Fixed bug in 'The Coward' where an enemy unit speaks as if he is on your side.
     * A bit of dialogue polishing in 'The Coward'
+ * units:
+   * balancing changes:
+     * switch the bat undead wariation to 'saurian'
 
 Version 1.3.8:
  * campaigns:

data/core/units/undead/Bat_Blood.cfg

@@ -13,6 +13,7 @@
     alignment=chaotic
     advanceto=null
     {AMLA_TOUGH 3}
+    undead_variation=saurian
     cost=21
     usage=scout
     unit_description= _ "Blood Bats are so-named because of their ruddy hue, which some mark as a symbol of their preferred diet. These creatures are fast and can drain the blood of those they attack, thereby gaining some of the health lost by their victims.

data/core/units/undead/Bat_Vampire.cfg

@@ -12,6 +12,7 @@
     level=0
     alignment=chaotic
     advanceto=Blood Bat
+    undead_variation=saurian
     cost=13
     usage=scout
     unit_description= _ "Vampire bats are flying beasts that feed on the blood of other creatures. While their fangs are not very powerful, the health of victims is drained away along with their blood, and given to the Bats.