Are you using a proxy for outbound traffic? It does not seem to be working correctly.
fatal: unable to access 'https://github.com/discourse/discourse.git/':
Received HTTP code 503 from proxy after CONNECT
Are you using a proxy for outbound traffic? It does not seem to be working correctly.
fatal: unable to access 'https://github.com/discourse/discourse.git/':
Received HTTP code 503 from proxy after CONNECT