Adds explicit status code 303 redirect to catalog#update

The redirect called in the catalog#update method is defaulting to a 302 redirect: http://api.rubyonrails.org/classes/ActionController/Redirecting.html#method-i-redirect_to

302's are notoriously non-SEO friendly... I believe the best way to do this is with a 303 redirect. After the initial post, the show route is requested via GET.