Update protobuf to 3.15.4#1492

pyup-bot wants to merge 1 commit intomasterkragniz/python-etcd3:masterfrom

pyup-update-protobuf-3.6.1-to-3.15.4kragniz/python-etcd3:pyup-update-protobuf-3.6.1-to-3.15.4Copy head branch name to clipboard