changelog: fix 1.4.2 release date

    $ git show 1.4.2
    commit 87cac5bd057ceafd6f779b1df33de61ca21b5e1d
    Author: Jeremy Ashkenas <jashkenas@gmail.com>
    Date:   Sat Oct 6 23:04:37 2012 -0400

        Underscore.js 1.4.2