routes: restore bare /year/month/date/slug blog route

We only switched to /blog in 2013, so there's a real chance
that old links would use the bare format. And it's not that
hard to match them and give them the same redirect.

config/routes.rb

@@ -59,6 +59,8 @@ Gitscm::Application.routes.draw do
 
   get "/blog" => "blog#index"
   get "/blog/*post" => redirect("/blog")
+  get "/:year/:month/:day/:slug" => redirect("/blog"),
+    :year => /\d{4}/, :month => /\d{2}/, :day => /\d{2}/
 
   get "/about" => "about#index"
   get "/about/:section" => "about#index"