Update your package search url as melpa.milkbox.net is now melpa.org

It's been a couple of days but the url has changed to melpa.org. You may need to change your .emacs file  from ("melpa" . "http://melpa.milkbox.net/packages/") to ("melpa" . "http://melpa.org/packages/")