fatal: unable to access 'https://github.com/protocolbuffers/protobuf.git/': Failed to connect to github.com port 443: Connection timed out
下载项目的时候出现了这个问题，本以为是网络或者什么的问题，没想到是sudo,sudo sudo git clone -b v3.6.1 https://github.com/protocolbuffers/protobuf.git就可以了