Debian Bullseye was released two days ago, and is now the default
distribution for the Docker image.
Our image isn't compatible with Debian Bullseye right now, and we
haven't done any testing with it, so for now we're staying with Buster.
Our Docker image uses Chromium v57, which is not supported by
chromedriver versions after 2.38. See
https://bugs.chromium.org/p/chromedriver/issues/detail?id=2445
The reason that the version of chromium is so old is that our base
image ruby:2.3.6 (the standard image for Ruby 2.3.6 on DockerHub) is
built on Debian 8 (jessie), which was made obsolete over a year ago.
The best solution is probably to upgrade the application to Ruby 2.3.7
(if not later), so we can use the official ruby:2.3.7 image, which is
kept up-to-date (it has Chromium 68).
Alternatively, we could try to install Chromium from a more up-to-date
repository, but this is probably not worth the trouble.
The following enhancements have been made to docker/docker-compose
* Fixed bug when building the image.
* docker-compose up starts the server
* Scaffolding inside the container respect the ownership of the files
outside it
* Volumes are tagged as 'delegated' in order to improve performance for
mac/windoze users.
* bundler stores packages in a volume. This whay new packages can be
added without rebuilding the image:
```bash
docker-compose run app bundle install
```
