fix: handling invalid gym environment

examples/gym-random-hunter.py

@@ -3,6 +3,7 @@
 import argparse
 import json
 
+# Register the Wumpus world environment
 import gym_wumpus
 from gym_wumpus.envs import WumpusEnv
 
@@ -45,7 +46,7 @@ def main():
         except error.Error as e:
             print('Bad Gym environment {}, using {}. Error is {}'.format(args.id, default_env, e))
             env = make(default_env)
-    if isinstance(env, WumpusEnv):
+    if hasattr(env, 'space_to_percept'):
         run_episode(env)
     else:
         print('Environment {} is not a Wumpus world.'.format(env))