updated mlagents to 2.3.0-exp

[alhasacademy96]

@kozzy97 @JohnBurden

Updated project settings in AAI3 project:

• Set required version of mlagents to 0.30.0, as per documentation of mlagents (Python),
• Set required version of ml-agents-envs to 0.30.0 (Python),
• Set required version of gym-unity to 0.30.0 (Python),
• Set required version of Python to at least 3.6.x, as per documentation of mlagents.
• Tested compatibility with unity engine build - all green.

Full changes (look for Release 20): https://github.com/Unity-Technologies/ml-agents/releases/tag/release_20

Nota Bene/TL;DR: the project now has accurate dependency requirements which reflects the changes in upgrading mlagents to 2.3.0 from 2.1.0.