Fix for MemoryS7 environment bug flagged by Johathan Binas

gym_minigrid/envs/memory.py

@@ -67,7 +67,7 @@ class MemoryEnv(MiniGridEnv):
 
         # Place objects
         start_room_obj = self._rand_elem([Key, Ball])
-        self.grid.set(3, height // 2 - 1, start_room_obj('green'))
+        self.grid.set(1, height // 2 - 1, start_room_obj('green'))
 
         other_objs = self._rand_elem([[Ball, Key], [Key, Ball]])
         pos0 = (hallway_end + 1, height // 2 - 2)