Apple is preparing a revised version of its AirPort Express 802.11n base station, according to a new report. Citing a person familiar with the matter, AppleInsider reports that the current model is out-of-stock or otherwise listed as discontinued at some third-party retailers, and that AirPort Utility—currently in development—specifically lists “Adds support for the AirPort Express 802.11n (2nd Generation) base station” in…