Add render_mode='rgb_array'

[Fernando Ribeiro]

Hi,

Some algorithms uses rgb_array render mode.

env = gym.make(env_id, render_mode='rgb_array')

I'm getting error:

gym_anytrading/envs/trading_env.py", line 29, in __init__ assert render_mode is None or render_mode in self.metadata['render_modes']

Thanks