Update 3_2_release_notes.md

Fixed typo and applied proper code highlighting.
Missing destroy command
Fix typos: the indefinite articles(a -> an)
Merge pull request #12216 from suginoy/a-an

Fix typos: the indefinite articles(a -> an).
Merge pull request #12215 from harshadsabne/master

Update 3_2_release_notes.md
Custom flash should be defined only for the class that defines it and it's subclasses.
Merge pull request #12222 from rcillo/fix-custom-flash

Custom flash should be defined only for the class that defines it and it's subclasses

Fixes #12057
Don't require using application_name before options

Before this commit options for `rails new` and `rails plugin new` had to
be passed in a strict order, trying to execute a following command:

    rails new -J path/to/app

resulted in an error.

This commit fixes the situation and allows to pass path to app anywhere
after `new`
Fixing comment typo in ActionController::Base
Merge pull request #12223 from adomokos/fixing_typo

Fixing comment typo in ActionController::Base
Removing ActiveSupport::Concern, it's not needed
Merge pull request #12225 from adomokos/no_need_for_active_support_concern

Removing ActiveSupport::Concern, it's not needed