fix: superclass RainbowAgent does not have min_q_weight in its __init__.

[qqpann]

I don't know what version of Dopamine you are using, but the superclass RainbowAgent does not have min_q_weight in its constructor.

This will cause an error running your example command:

TypeError: __init__() got an unexpected keyword argument 'min_q_weight'
  In call to configurable 'RainbowAgent' (<class 'dopamine.agents.rainbow.rainbow_agent.RainbowAgent'>)
  In call to configurable 'QuantileAgent' (<class 'batch_rl.multi_head.quantile_agent.QuantileAgent'>)
  In call to configurable 'FixedReplayQuantileAgent' (<class 'batch_rl.fixed_replay.agents.quantile_agent.FixedReplayQuantileAgent'>)
  In call to configurable 'Runner' (<class 'dopamine.discrete_domains.run_experiment.Runner'>)
  In call to configurable 'FixedReplayRunner' (<class 'batch_rl.fixed_replay.run_experiment.FixedReplayRunner'>)