Ignore /rails/mailers in route constraint

In addition to calls to `/rails/info`, ignore calls to `/rails/mailers`.

If a third `/rails` sub route becomes an issue, consider ignoring all
`/rails/*` routes.

CHANGELOG.md

@@ -1,9 +1,11 @@
 master
 ------
 
+* Ignore calls to `/rails/mailers`. [#520]
 * Call `render` with `html:` instead of `text:`. [#519]
 * Use `Mime::Type.html?` [#523]
 
+[#520]: https://github.com/thoughtbot/ember-cli-rails/pull/520
 [#519]: https://github.com/thoughtbot/ember-cli-rails/pull/519
 [#523]: https://github.com/thoughtbot/ember-cli-rails/pull/523
 

lib/ember_cli/ember_constraint.rb

@@ -7,7 +7,7 @@ def matches?(request)
     private
 
     def rails_info_request?(request)
-      request.fullpath.start_with?("/rails/info")
+      request.fullpath.start_with?("/rails/info", "/rails/mailers")
     end
 
     def html_request?(request)