If the expiring_url method is used when the storage is S3 or fog, the filesystem is no longer an option, since it doesn't declare this method. This situation forces you to use the cloud storage option in all the environments.
Having this simple alias allows you to use S3 or fog for production, and keep using the filesystem option for development and/or testing.
Add expiring_url as an alias for url
This makes a lot of sense, but can you add a test for it?
Add a test for expiring_url within filesystem storage
should I care about the Travis build result? I don't get those errors when running the test suite locally...
Merge remote-tracking branch 'upstream/master'
No, the tests pass for me too, so it's fine. Thanks for this, merged it in!