message: Fix mypy type error
diff: # Derived from: https://github.com/udacity/deep-reinforcement-learning/blob/master/dqn/solution/dqn_agent.py # pylint: disable-msg=line-too-long
  import random
  +from typing import cast
  import numpy as np
  import torch
  @@ -106,7 +107,7 @@ class TorchAgent(Agent):
  # Sample from transition buffer
  experiences = self.buffer.sample(k=self.batch_size)
  states, actions, rewards, next_states, dones = experiences
  - dones_bytes: torch.Tensor = dones.type(torch.uint8)
  + dones_bytes = cast(torch.Tensor, dones.type(dtype=torch.uint8))
  # Compute Q(s_t, a): Model computes Q(s_t), then we select the columns of actions taken
  state_action_values = self.dqn_policy(states).gather(1, actions)
  