Lower combat tank defualt speed

They are a bit fast, and the game is a bit fast.

mods/d2k/rules/vehicles.yaml

@@ -213,13 +213,13 @@ QUAD.starport:
 	Armor:
 		Type: Heavy
 	Mobile:
-		Speed: 7
+		Speed: 6
 		ROT: 6
 		Crushes: crate, infantry
 	RevealsShroud:
 		Range: 7
 	Turreted:
-		ROT: 5
+		ROT: 6
 		AlignWhenIdle: true
 	Armament:
 		Weapon: 90mm