Preping to build Mastodon on Docker. It seems that I have to make a mess on local clone to be able to run `rake secret` before I can run docker-compose build.
$ sudo apt install libpq-dev protobuf-compiler libprotobuf-dev pkg-config nodejs
$ rbenv install 2.4.1
$ rbenv local 2.4.1
$ gem install bundler
$ bundle install --path=vendor/bundle