Update TrainingProfile.py

[diditforlulz273]

Currently game_env_cls is hardcoded in TrainingProfile class, which allows to run any limit-based game by passing to Driver an instance of TrainingProfile with a parameter like game_cls=Flop5Holdem. However, passing game_cls=DiscretizedNLHoldem or any other not limit based game class will result in an error. Proposing to make game_env_cls accessible outside of TrainingProfile as a starting parameter and set a default(init) value to "FlatLimitPokerEnvBuilder" to keep provided examples' work correct.