Upgraded rack
As Rack has some non backwards compatible changes added required
modifications to keep behaviour in rails close to same as before.

Also modified generators to include rack/rack for not yet released
version of rack
Since upgrading rack we can remove unnecessary string encodings
https://github.com/rack/rack/commit/5a5aee36
Added rollback method to ActiveModel::Dirty
[Postgresql tests] remove duplicate helper
Merge pull request #15957 from seuros/duplicate

[Postgresql tests] remove duplicate helper
Rename options param of #time_ago_in_words to match API change

Rename `include_seconds_or_options` to `options` to match 6b9356a (which removed the deprecation introduced by #6077).  This has no functional impact because the parameter is passed directly through, but makes it clearer that the parameter no longer supports a boolean as input.
Always pass a column with a type object to quote

The only case where we got a column that was not `nil`, but did not
respond to `cast_type` was when type casting the default value during
schema creation. We can look up the cast type, and add that object to
the column definition. Will allow us to consistently rely on the type
objects for type casting in all directions.
Add punctuation and fix capitalization in Getting Started guide

Fix more small grammar mistakes in the [Getting Started guide](http://edgeguides.rubyonrails.org/getting_started.html#security), in sections 9 and 10.

Specifically, within sections 9.1 “Basic Authentication”, 9.2 “Other Security Considerations”, and 10 “What's Next?”.

“Rails Guides” is generally capitalized on the site, including on the linked page and in the title of the site, so I capitalized it.

“The” is not part of the name of the Ruby on Rails Security Guide – “The” is not in the title on that page.

And I added a missing period and a missing colon at the ends of two sentences.
[ci skip] Fix router option reference in 4.2 release notes.
Merge pull request #15964 from JuanitoFatas/doc/patch-01

[ci skip] Fix router option reference in 4.2 release notes.
Merge pull request #15963 from roryokane/getting-started-guide-fix-grammar

Add punctuation and fix capitalization in Getting Started guide
Merge pull request #15962 from sgrif/sg-types-for-defaults

Always pass a column with a cast_type to quote
Merge pull request #15961 from mckramer/patch-1

Rename options param of #time_ago_in_words to match API change
Quick pass through Active Support and guides CHANGELOG

[ci skip]
Tiny documentation fixes [ci skip]
Don't encourage usage of `columns_hash`

As discussed in https://github.com/plataformatec/simple_form/pull/1094,
we should not encourage usage of `columns_hash`, and instead provide an
alternate method to determine whether or not an attribute exists.

The language `attribute` was chosen over `column` since these are in the
`AttributeMethods` module.
Use the type object for sending JSON to the database
Add `Hash#map_values` to ActiveSupport

Didn't get a chance to convert existing code, I'll skim through the code
base to make use of this later this afternoon.
Merge pull request #15819 from sgrif/sg-hash-map-values

Add `Hash#map_values` to ActiveSupport to simplify a common pattern
Simplify creation of default attributes on AR instance

`AttributeSet#dup` has all the behavior we need.