Define new dependencies as a separate group

This allows user to exclude this from the bundle and also gives us the
option to define the group as optional some time later.

.travis.yml

@@ -39,7 +39,7 @@ cache:
     - frontend/node_modules
     - frontend/bower_components
 
-bundler_args: --without development production
+bundler_args: --without development production docker
 
 branches:
   only:

Gemfile

@@ -233,9 +233,12 @@ group :opf_plugins do
   gem 'openproject-translations', git:'https://github.com/opf/openproject-translations.git', branch: 'release/5.0'
 end
 
+# TODO: Make this group :optional when bundler v10.x
+# is matured enough that we can use this everywhere
+# http://bundler.io/blog/2015/06/24/version-1-10-released.html
+group :docker do
   gem 'passenger'
 
-group :production do
   # Used to easily precompile assets
   gem 'sqlite3', require: false
   gem 'rails_12factor', require: !!ENV['HEROKU']

doc/operation_guides/manual/installation-guide.md

@@ -146,7 +146,7 @@ with OpenProject. For more information, see https://github.com/opf/openproject-c
 [openproject@host] git clone https://github.com/opf/openproject-ce.git --branch stable/5 --depth 1
 [openproject@host] cd openproject-ce
 [openproject@host] gem install bundler
-[openproject@host] bundle install --deployment --without postgres sqlite development test therubyracer
+[openproject@host] bundle install --deployment --without postgres sqlite development test therubyracer docker
 [openproject@host] npm install
 ```