apostrophe hotfix for pretty PDF URLs, and a content-upgrader bug fix

[boutell]

Two small in-between updates:

We've released apostrophe version 4.28.1. This fixes a bug in the recently shipped support for optional "pretty URLs" for PDFs. That bug prevented the correct URL from being generated when locales have a custom prefix, like /fr.

We've also released @apostrophecms/content-upgrader version 1.1.2. This release correctly implements the --drop flag, which now drops the A4 database collections before importing A2 content again, just like it says on the label.