undefined method `helper' for ActionController::API:Class (NoMethodError)

```
.../.rvm/gems/ruby-2.5.1/gems/facebook_dialog-0.0.8/lib/facebook_dialog/railtie.rb:6:in `block in <class:Railtie>': undefined method `helper' for ActionController::API:Class (NoMethodError)
```

```helper``` method in railtie.rb is causing NoMethodError error for rails 5.

Please see #1 