This reverts commit ac74e2c5, reversing
changes made to ffdb0613.

We locked Minitest to 5.11.1 in #31799
because 5.11.2 included a breaking change.
The change was fixed in 5.11.3, so we no
longer need to lock in the version.

To workaround `undefined method `error?' for` reported
at https://travis-ci.org/rails/rails/jobs/333456146

This will avoid the branch being deleted by mistake making all builds to
fail.

Queue_classic currently limits pg to "< 0.20".
It is therefore not used for rails CI tests. There has been
a bull request for a while (by a co-worker of mine), which
fixes the incompatibilities and extends dependencies to pg-1.x.

This patch add this pull request to the Gemfile as an interim
solution, until it is merged.

Seems some tests not work with Minitest 5.11.0.

* https://travis-ci.org/rails/rails/jobs/323997512#L1053
* https://travis-ci.org/rails/rails/jobs/323997486#L1055

Ref: https://github.com/seattlerb/minitest/issues/729

Ref: https://github.com/collectiveidea/delayed_job/blob/master/CHANGELOG.md#414---2017-12-29

For pass Active Job integration tests with Ruby 2.5.
Ref: https://github.com/collectiveidea/delayed_job/pull/996

Follow up of #31432.

The v4.3.1 has already released that includes Redis 4.0 support.
https://github.com/resque/resque-scheduler/blob/master/CHANGELOG.md#431---2017-11-20

The `keyfile` was renamed to `credentials` in `google-cloud-storage` 1.8.0.
https://github.com/GoogleCloudPlatform/google-cloud-ruby/blob/master/google-cloud-storage/CHANGELOG.md#180--2017-11-14

Although `keyfile` can still be used, but it looks like deprecate.
https://github.com/GoogleCloudPlatform/google-cloud-ruby/blob/ddf7b2a856d676316525eb581c1a4cc83ca6097b/google-cloud-storage/lib/google/cloud/storage.rb#L589...L590

Therefore, I think that should use `credentials` in newly generated
applications.

Ref: https://github.com/GoogleCloudPlatform/google-cloud-ruby/issues/1802

This reverts commit 536d3068.

`em-hiredis` is unused since 48766e32

Move back to resque-scheduler mainline now that https://github.com/resque/resque-scheduler/pull/620 is merged

The `redis-namespace` 1.6.0 includes redis-rb 4.0 support.

Reverts 4d96be1c
References #31026

```ruby
TestHelperMailerTest#test_encode
BaseTest#test_implicit_multipart_with_attachments_creates_nested_parts
BaseTest#test_implicit_multipart_with_attachments_and_sort_order
BaseTest#test_explicit_multipart_with_attachments_creates_nested_parts
```
Refer https://travis-ci.org/rails/rails/jobs/295571582

This has been added by 8f8cb1ba.
But now it is unnecessary because it is not used in the test.

The sidekiq 5.0.5 includes redis-rb 4.0 support.
Ref: https://github.com/mperham/sidekiq/blob/90db3b84208cbb73a50d1a77a1dea97d3490ce70/Changes.md#505

* Use `gem 'redis', '~> 4.0'` for new app Gemfiles
* Loosen Action Cable redis-rb dep to `>= 3.3, < 5`
* Bump redis-namespace for looser Redis version dep
* Avoid using the underlying `redis.client` directly
* Use `Redis.new` instead of `Redis.connect`

Most interesting to us, 2.4.2 and 2.3.5 include the fix for
https://bugs.ruby-lang.org/issues/13632

`qu-redis` is need for qu adapter test.
However, since 8ecc5ab1, qu adapter test has not been executed,
it is unnecessary now.

I'm not sure this is the problem we're seeing on Travis (occasional
unexpected IOError exceptions), but it's worth a try.