Missing new line in error message

[justin808]

Without this, the error prints like this:

DEPRECATION WARNING: The asset "application.js" is not present in the asset pipeline.Falling back to an asset that may be in the public folder.
This behavior is deprecated and will be removed.
To bypass the asset pipeline and preserve this behavior,
use the `skip_pipeline: true` option.

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @rafaelfranca (or someone else) soon.

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