When I was creating tests for the generator errors, I noticed I could not get the application.scss exist? error to show up when skipping the creation of it in the test setup using application_css: false

Here we check if application.scss exists:
https://github.com/shakacode/react_on_rails/blob/master/lib/generators/react_on_rails/bootstrap_generator.rb#L56

However, it will always exist because of the previous method above it, so it's impossible to get the error:

https://github.com/shakacode/react_on_rails/blob/master/lib/generators/react_on_rails/bootstrap_generator.rb#L23

Do you think the add error is necessary?

(cc: @robwise)