In f6e293ec we avoided a segfault in the
tests, however I think we should try to avoid the crash, as it may
happen in user code as well.

Here is what I distiled the bug down to:

```ruby
# Rails case - works on 2.0, 2.1; crashes on 2.2
require 'action_dispatch'

ActionDispatch::Response.new(200, "Content-Type" => "text/xml")

# General case - works on 2.0, 2.1; crashes on 2.2
def foo(optional = {}, default_argument: nil)
end

foo('quux' => 'bar')
```

Actually, our app has 400,000 LOC 💥

Introduced in f6e293ec ActionPack tests began sefaulting. I found that it
was the kwargs and the test causing the seg fault was missing the new
default_headers argument.

[ci skip] Fix fenced code block lang

Update link (minor fix)

Minor fixes (proposal)

Reduce allocated memory for Module#delegate.

[ci skip] Add code examples for Module#anonymous? documentation

[ci skip] Fix to comment

[ci skip] Fix to String

[ci skip] Update documentation for Range#to_formatted_s

created rake restart task

add `ActiveJob::TestCase` to list of classes providing for test [ci skip]

[ci skip] Remove `,`

[skip ci] Add documentation for String#is_utf8? method

[ci skip]

[ci skip] Replace `ActiveResource` with `Active Resource`

Update documentation examples for String#remove [skip ci]

[ci skip] Fix table of 4_1_release_notes.md

Remove reference to workingwithrails.com since it is being retired

Removed non-standard and unused require 'active_support/deprecation'

It is very slow since it will precompile even plugins.

Also it is very unlikely that any application will use this patterns
since it is not a good practice to include all assets manually in the
page.

[ci skip]

Removed non-standard and unused require 'active_support/deprecation' from parts out of active_support.