`ActionDispatch::Head` was replaced by `Rack::Head`. Closes #14191.

See 449039a86d802871b707dfb51ac1ed96d53526f9 for the original commit.
Add missing parantheses in index_exists?
Point master changelogs to 4-1-stable branch

Remove 4-1 related entries from master [ci skip]
Merge pull request #14193 from ys/patch-1

Add missing parantheses in index_exists?
Fix Generation of proper migration when
    ActiveRecord::Base.pluralize_table_names = false.

    Previously, generation a migration like this:

        rails g migration add_column_name_to_user name

    would not generating the correct table name.