Install protoc on macOS:
PROTOC_ZIP=protoc-3.14.0-osx-x86_64.zip
curl -OL https://github.com/protocolbuffers/protobuf/releases/download/v3.14.0/$PROTOC_ZIP
sudo unzip -o $PROTOC_ZIP -d /usr/local bin/protoc
sudo unzip -o $PROTOC_ZIP -d /usr/local 'include/*'
rm -f $PROTOC_ZIP
from: http://google.github.io/proto-lens/installing-protoc.html