New CSSBundling compilation fails in production

[briri]

Depending on how the application is deployed to production, the CSSBundling compilation step can fail silently. This results in the system returning a 500 error due to the public/assets/application-[fingerprint].css not existing.

According to the CSSBundling docs you need to add a .gitkeep file to the app/assets/builds/ directory so that it exists when deploying the application.

There is currently an exception in the .gitignore for a app/assets/builds/.keep but the file does not exist in the directory

[aaronskiba]

It appears that #3314 resolved this issue. Closing it now.