Jason Kim The gifts are wrapped; the decorations are organized; the RSVPs are sent. All that’s left on your holiday to-do list is finding a last-minute present for yourself: an updated party dress. If upcoming dinner parties and gift exchanges make you want to really get dressed up again, there’s still time to add a new look to your lineup. The key is Amazon’s best holiday dresses. After combing through hundreds of Amazon listings, we’ve found a bevy of dresses from the understated to the Instagrammable: a satin Vince slip dress for the minimalists, a taffeta Cynthia Rowley confection for the maximalists, and dresses by Dundas, Free People, and more…