Fix VecEnv docstrings (closes #577)

docs/misc/changelog.rst

@@ -63,6 +63,7 @@ Others:
 - Minor PEP8 fixes in dqn.py (@justinkterry)
 - Add a message to the assert in `PPO2`
 - Update replay buffer doctring
+- Fix `VecEnv` docstrings
 
 Documentation:
 ^^^^^^^^^^^^^^

stable_baselines/common/vec_env/dummy_vec_env.py

@@ -12,7 +12,8 @@ class DummyVecEnv(VecEnv):
     multiprocess or multithread outweighs the environment computation time. This can also be used for RL methods that
     require a vectorized environment, but that you want a single environments to train with.
 
-    :param env_fns: ([Gym Environment]) the list of environments to vectorize
+    :param env_fns: ([callable]) A list of functions that will create the environments
+        (each callable return a `Gym.Env` instance when called).
     """
 
     def __init__(self, env_fns):

stable_baselines/common/vec_env/subproc_vec_env.py

@@ -62,7 +62,8 @@ class SubprocVecEnv(VecEnv):
         ``if __name__ == "__main__":`` block.
         For more information, see the multiprocessing documentation.
 
-    :param env_fns: ([Gym Environment]) Environments to run in subprocesses
+    :param env_fns: ([callable]) A list of functions that will create the environments
+        (each callable return a `Gym.Env` instance when called).
     :param start_method: (str) method used to start the subprocesses.
            Must be one of the methods returned by multiprocessing.get_all_start_methods().
            Defaults to 'forkserver' on available platforms, and 'spawn' otherwise.