[NFP] Minor bug - Great Wall Description of Zombie MOD

[cholsy]

From GS, <LOC_IMPROVEMENT_GREAT_WALL_EXPANSION2_DESCRIPTION> is used, instead of <LOC_IMPROVEMENT_GREAT_WALL_DESCRIPTION>.
That's why {LOC_DESCRIPTION_ADDENDUM_BARRICADE} does not appear in GS.

Following code is recommended for GS player.

UPDATE Improvements SET Description='LOC_IMPROVEMENT_GREAT_WALL_DESCRIPTION_ZOMBIE'
WHERE  Description='LOC_IMPROVEMENT_GREAT_WALL_EXPANSION2_DESCRIPTION';