Patch for newer Rails versions not supporting text option for render

Calling `render text: ...` has been deprecated in `rails@5.1`.

This commit [replaces `text:` with `html:`][docs].

[docs]: http://guides.rubyonrails.org/layouts_and_rendering.html#rendering-html

CHANGELOG.md

@@ -1,8 +1,10 @@
 master
 ------
 
-* Use `Mime::Type.html?`
+* Call `render` with `html:` instead of `text:`. [#519]
+* Use `Mime::Type.html?` [#523]
 
+[#519]: https://github.com/thoughtbot/ember-cli-rails/pull/519
 [#523]: https://github.com/thoughtbot/ember-cli-rails/pull/523
 
 0.8.4

app/helpers/ember_rails_helper.rb

@@ -8,6 +8,6 @@ def render_ember_app(name, &block)
 
     head, body = markup_capturer.capture
 
-    render text: EmberCli[name].index_html(head: head, body: body).html_safe
+    render html: EmberCli[name].index_html(head: head, body: body).html_safe
   end
 end