* Update to support the Food Collector environment
Recently, I am trying out ML Agent with Ray, and trying to use the food collector environment. Since the observation space and action space haven't defined in the unity3d_env.py. I propose to make this changes to add the support for Food Collector. I have tried to use this env in the [unity3d_env_local example](https://github.com/ray-project/ray/blob/master/rllib/examples/unity3d_env_local.py). Please let me know if this the proper adjustment. Even these are just few line of code, please let me know how can I made a proper contribution.
* Apply suggestions from code review
