mix deps.get timeout 问题：
If this happens consistently, adjust your concurrency and timeout settings:
HEX_HTTP_CONCURRENCY=1 HEX_HTTP_TIMEOUT=120 mix deps.get解决方法：
HEX_HTTP_CONCURRENCY=3 HEX_HTTP_TIMEOUT=1200 mix deps.get
备注：实际上就是使用环境变量