Updating documentation links (#411)

Co-authored-by: Mark Towers <mark.m.towers@gmail.com>

minigrid/envs/wfc/wfcenv.py

@@ -56,7 +56,7 @@ class WFCEnv(MiniGridEnv):
     - Each tile is encoded as a 3 dimensional tuple:
         `(OBJECT_IDX, COLOR_IDX, STATE)`
     - `OBJECT_TO_IDX` and `COLOR_TO_IDX` mapping can be found in
-        [minigrid/minigrid.py](minigrid/minigrid.py)
+        [minigrid/core/constants.py](minigrid/core/constants.py)
     - `STATE` refers to the door state with 0=open, 1=closed and 2=locked
 
     ## Rewards