Added robofac_gun.json

Properly adding a necessary file to ensure that the grip mods are consistently blacklisted between each other.

data/json/items/gun/robofac_gun.json

@@ -397,6 +397,7 @@
     "type": "GUNMOD",
     "copy-from": "grip",
     "name": { "str": "integrated front grip" },
+	"blacklist_mod": [ "offset_grip" ],
     "flags": [ "PUMP_RAIL_COMPATIBLE", "IRREMOVABLE" ]
   },
   {