Fix EmberCli::EmberController inheritance

The `EmberCli::EmberController` used to inherit from
`ApplicationController` in order to reap the benefits of
application-wide configurations and behavior (such as
authentication-based `before_action` calls and other macros).

Unfortunately, with the introduction of Rails 5's `rails new --api`,
applications' `ApplicationController` can now inherit from
[`ActionController::API`][api], which doesn't serve HTML by default.

To support Rails 5's default `--api` behavior,
`EmberCli::EmberController` must inherit from `ActionController::Base`,
forcing the controller to forfeit all the benefits of sharing behavior
with `ApplicationController`.

Author: seanpdoyle

CHANGELOG.md

@@ -1,6 +1,8 @@
 master
 ------
 
+* `EmberCli::EmberController` now inherits from `ActionController::Base` instead
+  of `ApplicationController`. [#400]
 * Remove support for Ruby 2.1.x. [#400]
 * Enhance `rake ember:install` to fully reinstall if necessary. [#396]
 * `EmberCli::Deploy::File` serves assets with Rails' `static_cache_control`

app/controller/ember_cli/ember_controller.rb

@@ -1,5 +1,5 @@
 module EmberCli
-  class EmberController < ::ApplicationController
+  class EmberController < ActionController::Base
     def index
       render layout: false
     end