Fix the name of the environment in README

[shagunsodhani]

Current stack trace

python -m nle.scripts.play --env nethack
Traceback (most recent call last):
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/site-packages/nle/scripts/play.py", line 238, in <module>
    main()
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/site-packages/nle/scripts/play.py", line 234, in main
    play(**vars(flags))
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/site-packages/nle/scripts/play.py", line 82, in play
    env = gym.make(env_name, savedir=savedir, max_episode_steps=max_steps)
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/site-packages/gym/envs/registration.py", line 145, in make
    return registry.make(id, **kwargs)
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/site-packages/gym/envs/registration.py", line 89, in make
    spec = self.spec(path)
  File "/private/home/sodhani/.conda/envs/nle/lib/python3.8/site-packages/gym/envs/registration.py", line 118, in spec
    raise error.Error('Attempted to look up malformed environment ID: {}. (Currently all IDs must be of the form {}.)'.format(id.encode('utf-8'), env_id_re.pattern))
gym.error.Error: Attempted to look up malformed environment ID: b'nethack'. (Currently all IDs must be of the form ^(?:[\w:-]+\/)?([\w:.-]+)-v(\d+)$.)

After the fix

 python -m nle.scripts.play --env NetHackScore-v0
Available actions: (<MiscAction.MORE: 13>, <CompassDirection.N: 107>, <CompassDirection.E: 108>, <CompassDirection.S: 106>, <CompassDirection.W: 104>, <CompassDirection.NE: 117>, <CompassDirection.SE: 110>, <CompassDirection.SW: 98>, <CompassDirection.NW: 121>, <CompassDirectionLonger.N: 75>, <CompassDirectionLonger.E: 76>, <CompassDirectionLonger.S: 74>, <CompassDirectionLonger.W: 72>, <CompassDirectionLonger.NE: 85>, <CompassDirectionLonger.SE: 78>, <CompassDirectionLonger.SW: 66>, <CompassDirectionLonger.NW: 89>, <MiscDirection.UP: 60>, <MiscDirection.DOWN: 62>, <MiscDirection.WAIT: 46>, <Command.KICK: 4>, <Command.EAT: 101>, <Command.SEARCH: 115>)
Previous reward: 0.0
b'Hello Agent, welcome to NetHack!  You are a neutral male human Monk.'
an uncursed +2 pair of leather gloves (being worn)
an uncursed +1 robe (being worn)
a blessed spellbook of protection
an uncursed scroll of identify
2 uncursed potions of healing
a blessed potion of healing
3 uncursed food rations
5 uncursed apples
6 uncursed oranges
3 uncursed fortune cookies
an uncursed oil lamp





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[heiner]

Thanks!