Add carriage return to end of appended line

[jcoyne]

Fixes #3031

[sandbergja]

Thanks, @jcoyne ! This got me just to my next error:

Multiple files with the same output path cannot be linked ("application.js")
In "/Users/sandbergj/tmp/search_app-fixed/app/assets/config/manifest.js" these files were linked:
  - /Users/sandbergj/tmp/search_app-fixed/app/assets/javascripts/application.js
  - /Users/sandbergj/tmp/search_app-fixed/app/javascript/application.js

If I simply remove the line //= link application.js from manifest.js, it works again.

The generator made an app using importmap-rails 1.1.5 and sprockets 4.2.0, for what it's worth.

[jcoyne]

I believe the double link error is because Blacklight 7.33 is not compatible with importmap, which is what rails 7 installs by default.