So, Dependabot correctly reported that this version of puma is
vulernable, which I fixed in the main app already—but I didn't notice we
also use that version in this cute tiny placeholder app we use early in
the deployment process.
There's not a real security need to upgrade this, as this placeholder
app has no access to useful data when it is run, but I think it's better
to resolve this by fixing it than by silencing Dependabot! May as well!
Yay it's working! We set up the box, install Ruby, upload a placeholder app, set it up as a service, and get it hooked up to nginx!
Next, we'll add the script to upload the latest version of the site. We just need to slot it into `/srv/impress/current`, run `bundle install`, and that should basically be that! (Oh, and we need to compile production assets—I wonder if it's useful to do that on the dev machine instead of on the target? That might save us from needing to install Node. Or maybe we'll have to anyway!)
