Solution:
use the Carbon class included with Laravel 4.2
At the top of the file, put this:
use Carbon\Carbon;
Here’s the query
$post = DB::update('UPDATE posts SET title=?,message=?,author=?,updated_at=? WHERE id=?',
array(
Input::get('title'),
Input::get('message'),
Input::get('author'),
\Carbon\Carbon::now(),
$id
)
);