Increased max_steps on Empty & DoorKey envs

This is necessary because goal is harder to reach now that we've
added more actions.

gym_minigrid/envs/doorkey.py

@@ -7,7 +7,10 @@ class DoorKeyEnv(MiniGridEnv):
     """
 
     def __init__(self, size=8):
-        super().__init__(grid_size=size, max_steps=4 * size)
+        super().__init__(
+            grid_size=size,
+            max_steps=10*size
+        )
 
     def _gen_grid(self, width, height):
         # Create an empty grid

gym_minigrid/envs/empty.py

@@ -9,7 +9,7 @@ class EmptyEnv(MiniGridEnv):
     def __init__(self, size=8):
         super().__init__(
             grid_size=size,
-            max_steps=3*size,
+            max_steps=5*size,
             # Set this to True for maximum speed
             see_through_walls=True
         )