Fix benchmarking Atari domains in parallel

[danijar]

Exception in thread Thread-21:
Traceback (most recent call last):
  File "/usr/lib/python3.4/threading.py", line 920, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.4/threading.py", line 868, in run
    self._target(*self._args, **self._kwargs)
  File "/home/dhafner/repository/vizbot/vizbot/core/trainer.py", line 66, in target
    self._run_episode(env, learner, training=True)
  File "/home/dhafner/repository/vizbot/vizbot/core/trainer.py", line 102, in _run_epis
ode
    agent.experience(*transition)
  File "/home/dhafner/repository/vizbot/vizbot/agent/dqn.py", line 61, in experience
    self._memory.append((state, action, reward, successor))
  File "/home/dhafner/repository/vizbot/vizbot/utility/experience.py", line 25, in appe
nd
    self._initialize(transition)
  File "/home/dhafner/repository/vizbot/vizbot/utility/experience.py", line 54, in _ini
tialize
    self._transitions = [np.empty(x) for x in shapes]
  File "/home/dhafner/repository/vizbot/vizbot/utility/experience.py", line 54, in <lis
tcomp>
    self._transitions = [np.empty(x) for x in shapes]
TypeError: an integer is required