Run CI for ActionPack on JRuby

Removes potentially quadratic Regexp from ActiveRecord::LogSubscriber…

Honour joining model order in `has_many :through` associations when
eager loading

Drop Action Controller require in ActionDispatch::ExceptionWrapper

Add documentation for #13897 [skip ci]

Fix value of CSS background-color property in Ruby on Rails guide

We only reference the Action Controller error classes by name in
ActionDispatch::ExceptionWrapper, so there is no need to explicitly
require them.

It drops a tiny coupling between Action Dispatch and Action Controller,
so it makes me feel warm inside. We still have a lot of others AC
requires in the AD code base, but here, we can save it.

[ci skip]

Having more readable test descriptions in railties actions_test.rb

Changed description with tests related to rails_command.

Fix typos in Rails guide about Action View Overview

This patch fixes some typos in the Action View Overview section of the Rails guide.

[ci skip]

Change background-color value to transparent, which is the default value of background-color.

[ci skip]

Address ruby warnings

- Ambiguous first argument
- Mismatched indentation

add `constraint_to` option to SSL middleware

Update deprecation message shown when tasks from rails namespace are run

Fix formatting in Action Cable guide [ci skip]

Fix merge conflict in Action Cable guide [ci skip]

remove "rake" word [ci skip]

Fix typos in Action Cable guide [ci skip]

Guide for Action Cable

Ensure actioncable behaves as expected with non-string queues

use `app:update` instead of deprecated `rails:update` [ci skip]

`rails:update` was deprecated in 6fb31638

[ci skip] Add small Action Cable documentation fixes

* Fix typos/grammar errors
* Make capitalization/naming consistent

This guides were pointing to this command `rails app:update`, which I
tried to run, but it didnt worked. I think the right command is `rails
rails:update` instead. Also thats the name of the rake task.

Also I removed the `Rake` word from the title, as we run it using
`rails` bin now.

cc @kaspth
[skip ci]

remove rack cors initializer when updating

These are green on local. Checking to see they pass on travis too!

Use app namespace for framework tasks