Replace update_all with update_attributes on each license key.

In the end it's too problematic to use an update_all here, since we need
callbacks to be run, etc. There are only ever a few license keys anyway
so this should not result in any serious performance issues.

Change-Id: Ib9e58103acc36cb41b332a9edadaf766a5fa9307
Merge pull request #1 from degica/replace_update_all

Replace update all