This rule is broken when we have ".,;::!?" in the headers.
We have removed the ones with ":" but kept the ones
with "?", so this rule will always warn in these cases.
This is the Ruby version CONSUL uses now. Thanks to that, we no longer
need to install an old version of libssl-dev for Ubuntu 18.04.
We could probably simplify the documentation using:
```bash
rbenv install `cat .ruby_version`
```
However, this would require downloading consul before installing Ruby,
which could be harder to document.
