For Err:
fatal: unable to access 'https://github.com/RaymondDixon/ml-agents.git/': Could not resolve proxy: proxy.domain.com
it means proxy is wrong.
In windows-Behind Firewall to setup proxy, Open GitBash type git config --list --show-origin to see where .gitconfig file is (usually in Users/username/.gitconfig)
type cd to be in then press enter
type vim .gitconfig then press enter