The goal here is to have a notion on what the defaults are in a Rails 5
application, know why our application is working in a different way
(it's because these defaults aren't loaded in an application which was
originally developed using Rails 4), and have an explicit list of things
we are overwriting.
Furthermore, running the `app:update` rake task to upgrade to Rails 5.2
will by default add the line loading default options for Rails 5.0, so
by adopting those default options we prevent accidental mistakes when
upgrading.
We'll have to review these items and see which ones can be changed to
their default values for Rails 5 applications.
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