Change from WEBrick to Puma

Ever since docker-library/redmine#261 the default uses puma instead of WEBrick.  Puma is considered production-ready whereas WEBrick was not recommended for production.

Author: petiepooo

redmine/content.md

@@ -48,7 +48,7 @@ Run `docker stack deploy -c stack.yml %%REPO%%` (or `docker-compose -f stack.yml
 
 ## Alternative Web Server
 
-The other tags in this repository, like those with `passenger`, use the same environment and `--links` as the default tags that use WEBrick (`rails s`) but instead give you the option of a different web and application server. `passenger` uses [Phusion Passenger](https://www.phusionpassenger.com/). [`tini`](https://github.com/krallin/tini) is used for reaping [zombies](https://en.wikipedia.org/wiki/Zombie_process).
+The other tags in this repository, like those with `passenger`, use the same environment and `--links` as the default tags that use Puma (`rails server`) but instead give you the option of a different web and application server. `passenger` uses [Phusion Passenger](https://www.phusionpassenger.com/). [`tini`](https://github.com/krallin/tini) is used for reaping [zombies](https://en.wikipedia.org/wiki/Zombie_process).
 
 ## Accessing the Application