Minor fixes for the resize observation wrapper (openai#254)

gymnasium/wrappers/resize_observation.py

@@ -49,11 +49,9 @@ def __init__(self, env: gym.Env, shape: tuple[int, int] | int) -> None:
         ), f"Expected the observation space to be Box, actual type: {type(env.observation_space)}"
         dims = len(env.observation_space.shape)
         assert (
-            2 <= dims <= 3
+            dims == 2 or dims == 3
         ), f"Expected the observation space to have 2 or 3 dimensions, got: {dims}"
 
-        self.shape = tuple(shape)
-
         obs_shape = self.shape + env.observation_space.shape[2:]
         self.observation_space = Box(low=0, high=255, shape=obs_shape, dtype=np.uint8)