Python3 Incompability for frozen_lake.py

[kevin00036]

Running gym with python3.5, task FrozenLake-v0, episodes never terminates even when the agent reaches 'H' or 'G'.

It seems there's some problem with python3 str/bytes.
For example, frozen_lake.py line 71:
isd = np.array(desc == 'S').astype('float64').ravel()
Comparison desc == 'S' will return a big pure python False, rather than a numpy array of booleans. Changing it to desc == b'S' works.
Lines 103, 104, 110, 111 also needs modification:

done = bytes(newletter).decode() in 'GH'
rew = float(newletter == b'G')

[gdb]

Good find. Would you be up for opening a pull request?