No longer needed workaround for Ruby 2.2 "private attribute?" warning.

Related 6d63b5e4.

Follow up ae406cd6.

Originally specified attributes were only normal values, and
`ActiveRecord::MultiparameterAssignmentErrors` did not occur.

In addition, an assertion is performed only on rescue, even if an
exception does not occur, the test passes. To avoid this use `assert_raise`.

Updates expires_in docs

Refactor migrations_path command option to database

Previously the documentation for expires_in suggested that the option
was available for all cache stores. This clarifies that the behavior can
be supported, but is not always supported.

* Documentation clarity in ActiveJob::TestHelper [ci skip]

* Documentation for options

[Mohit Natoo + Rafael Mendonça França]

Fix HashWithIndifferentAccess#without bug

Update backburner to the latest version

version 1.5.0 includes to warning fixes that show on tests:
https://github.com/nesquena/backburner/commit/cd9670146bca4df83ae2aacb95b3e6d1c1c1eee8
https://github.com/nesquena/backburner/commit/4dfa22bda1685ca1afa9f7d474df471ca6364e69

Update guide for validation custom contexts [ci skip]

Documentation for queue_adapter_name method in ActiveJob::QueueAdapter

[ci skip]

Bugfix ActiveRecord::Relation#merge special case of from clause

When one relation is merged into another that has a different base class
merging `from_clause` causes invalid SQL to be generated

LoggerSilence doesn't require concurrent:

- LoggerThreadSafeLevel does nowaday since 2518bda9

Clarify transactional behavior of after_commit and after_rollback callbacks

[ci skip]

[ci skip] Do not recommend testing stored object in template

Since `assigns` is not placed by default with Rails, we suggested to
test if the right information was displayed instead of suggesting to
test if the right object was stored in the template.

Do not enable disabled elements for XHR redirects

* Handle more unsafe String methods

* Fix codeclimate issue

* Revert stylistic change

[Janosch Müller + Rafael Mendonça França]

Add probot autolabeler config

[ci skip]

Fix optionally scoped root route unscoped access

Revert "record who created the node when $DEBUG is true"

Fixing an edge case when using objects as constraints

This PR fixes an issue when the following situation occurs.
If you define a class like this

    class MyConstraint
      def call(*args)
        # for some reason this is defined
      end

      def matches?(*args)
        # checking the args
      end
    end

and try to use it as a constraint

    get "/", to: "home#show", constraints: MyConstraint.new

if its `matches?` method returns `false` there will be an error for the
mapper will ask for the constraint arity, thinking it is a proc, lambda
or method.

This PR checks for the presence of the `arity` method on the constraint
calling it only if present, preventing the error while keeping the basic
behavior.

This reverts commit a1b72178.

Since Ruby 2.4 unified Fixnum and Bignum into Integer.

Before:

```
  Topic Update All (0.4ms)  UPDATE `topics` SET `topics`.`replies_count` = COALESCE(`topics`.`replies_count`, 0) + 1, `topics`.`updated_at` = '2018-09-27 18:34:05.068774' WHERE `topics`.`id` = ?  [["id", 7]]

```

After:

```
  Topic Update All (0.4ms)  UPDATE `topics` SET `topics`.`replies_count` = COALESCE(`topics`.`replies_count`, 0) + ?, `topics`.`updated_at` = ? WHERE `topics`.`id` = ?  [["replies_count", 1], ["updated_at", 2018-09-27 18:55:05 UTC], ["id", 7]]

```

Add a way to check for subset of arguments when performing jobs:

Remove Rails 5.0 workaround from ActionCable::Channel::TestCase

Add missing rdoc +code+ tags [ci skip]

Before:

```
  Pet Update All (0.8ms)  UPDATE `pets` LEFT OUTER JOIN `toys` ON `toys`.`pet_id` = `pets`.`pet_id` SET `pets`.`name` = 'Bob' WHERE `toys`.`name` = ?  [["name", "Bone"]]
```

After:

```
  Pet Update All (1.1ms)  UPDATE `pets` LEFT OUTER JOIN `toys` ON `toys`.`pet_id` = `pets`.`pet_id` SET `pets`.`name` = ? WHERE `toys`.`name` = ?  [["name", "Bob"], ["name", "Bone"]]
```