readd hexamine

Accidentally removed it in a conflict resolution.

data/json/itemgroups/Locations_MapExtras/locations_mapextras.json

@@ -165,6 +165,7 @@
       { "item": "camera", "prob": 15, "charges": [ 0, 150 ] },
       { "item": "camera", "container-item": "camera_bag", "prob": 5, "charges": [ 0, 150 ] },
       [ "camera_bag", 10 ],
+      [ "chem_hexamine", 5 ],
       { "group": "pillbox_any_used", "prob": 10 }
     ]
   },