`Capybara::RackTest::Driver` does not support taking screenshots. If call
`#save_screenshot` on `Capybara::RackTest::Driver` will raise the error.

```ruby
Error:
UsersTest#test_visiting_the_index:
Capybara::NotSupportedByDriverError: Capybara::Driver::Base#save_screenshot
```

To prevent errors, if driver does not support screenshot, do not call it.

Add iso8601 and rfc3339 parsing to timezones

For naming consistency when using the RFC 3339 profile
of ISO 8601 in applications.

The `Time.xmlschema` and consequently its alias `iso8601` accepts
timestamps without a offset in contravention of the RFC 3339
standard. This method enforces that constraint and raises an
`ArgumentError` if it doesn't.

Previously there was no way to get a RFC 3339 timestamp
into a specific timezone without either using `parse` or
chaining methods. The new method allows parsing directly
into the timezone, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.rfc3339("1999-12-31T14:00:00Z")
    => Fri, 31 Dec 1999 14:00:00 HST -10:00

This new method has stricter semantics than the current
`parse` method and will raise an `ArgumentError`
instead of returning nil, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.rfc3339("foobar")
    ArgumentError: invalid date
    >> Time.zone.parse("foobar")
    => nil

It will also raise an `ArgumentError` when either the
time or offset components are missing, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.rfc3339("1999-12-31")
    ArgumentError: invalid date
    >> Time.zone.rfc3339("1999-12-31T14:00:00")
    ArgumentError: invalid date

Previously there was no way to get a ISO 8601 timestamp into a specific
timezone without either using `parse` or chaining methods. The new method
allows parsing directly into the timezone, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.iso8601("1999-12-31T14:00:00Z")
    => Fri, 31 Dec 1999 14:00:00 HST -10:00

If the timestamp is a ISO 8601 date (YYYY-MM-DD) then the time is set
to midnight, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.iso8601("1999-12-31")
    => Fri, 31 Dec 1999 00:00:00 HST -10:00

This new method has stricter semantics than the current `parse` method
and will raise an `ArgumentError` instead of returning nil, e.g:

    >> Time.zone = "Hawaii"
    => "Hawaii"
    >> Time.zone.iso8601("foobar")
    ArgumentError: invalid date
    >> Time.zone.parse("foobar")
    => nil

Fix spelling in docs

[ci skip]

It turns out that we don't need to require system tests in the railties
test helper so we can remove it. If you're using system tests they will
be loaded by inheriting from ActionDispatch::SystemTestCase and the
routes will be loaded by ActionDispatch::IntegrationTest.

Remove `node` parameter to `join_constraints`

I don't think we actually need this parameter anymore.  Nobody seems to
be using it.

Fix random failure on system test with ajax

Deprecate implicit coercion of `ActiveSupport::Duration`

If application has ajax, browser may begin request after rollback.
`teardown_fixtures` will be called after `super` on `after_teardown`
so we must call `Capybara.reset_sessions!` before `super`

https://github.com/rails/rails/blob/b61a56541aecd7ac685d4f19d943177a3f1b465a/activerecord/lib/active_record/fixtures.rb#L857

Fix typo in Upgrading Ruby on Rails Guide

fixed suspected typo in sample sql query

Includes a script to ease an app's upgrade.

Update secrets to use modern crypto

Use `blank?` instead of `empty?`

In order to avoid `NoMethodError` when it is nil.

Follow up to 82f7dc61

Currently `ActiveSupport::Duration` implicitly converts to a seconds
value when used in a calculation except for the explicit examples of
addition and subtraction where the duration is the receiver, e.g:

    >> 2 * 1.day
    => 172800

This results in lots of confusion especially when using durations
with dates because adding/subtracting a value from a date treats
integers as a day and not a second, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 2 * 1.day
    => Mon, 10 Apr 2490

To fix this we're implementing `coerce` so that we can provide a
deprecation warning with the intent of removing the implicit coercion
in Rails 5.2, e.g:

    >> 2 * 1.day
    DEPRECATION WARNING: Implicit coercion of ActiveSupport::Duration
    to a Numeric is deprecated and will raise a TypeError in Rails 5.2.
    => 172800

In Rails 5.2 it will raise `TypeError`, e.g:

    >> 2 * 1.day
    TypeError: ActiveSupport::Duration can't be coerced into Integer

This is the same behavior as with other types in Ruby, e.g:

    >> 2 * "foo"
    TypeError: String can't be coerced into Integer
    >> "foo" * 2
    => "foofoo"

As part of this deprecation add `*` and `/` methods to `AS::Duration`
so that calculations that keep the duration as the receiver work
correctly whether the final receiver is a `Date` or `Time`, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 1.day * 2
    => Fri, 03 Mar 2017

Fixes #27457.

Update `DateTime#change` to support usec and nsec

Adding support for these options now allows us to update the
`DateTime#end_of` methods to match the equivalent `Time#end_of`
methods, e.g:

    datetime = DateTime.now.end_of_day
    datetime.nsec == 999999999 # => true

Fixes #21424.

Fixes #28135.

`valid_type?` should accept only supported types

Just dispatch to the command help itself for more info.

Prefer Thor's say method to Kernel's plain puts.

In case there's no $EDITOR assigned users would see a cryptic:

```
% EDITOR= bin/rails secrets:edit
Waiting for secrets file to be saved. Abort with Ctrl-C.
sh: /var/folders/wd/xnncwqp96rj0v1y2nms64mq80000gn/T/secrets.yml.enc: Permission denied
New secrets encrypted and saved.
```

That error is misleading, so give a hint in this easily detectable case.

Fixes #28143.

Use appropriate type for `test_framework` option

Use DEFAULT_CIPHER constant in MessageEncryptor

This fixes the following warning.

```
Expected string default value for '--test-framework'; got false (boolean)
```

Support for using `SELECT` column or expression aliases in the `HAVING`
clause isn't part of the SQL standard so it's better to whitelist the
test for adapters where we know it works and skip it on others.

`HOST` must be all capital letters