rails/rails — pull request #16113 by egilburg (2014-07-09 20:49:52+00:00)
Title: [ci skip] Document millisecond precision change in ActiveSupport::TimeWithZone#as_json

Before, `TimeWithZone#as_json` had no millisecond precision, and now it does. Since this may be a breaking change for some apps or API consumers, we should document this in the Upgrade Gudies.