Fix typo in routing guide

Update the tip in section 4.8 of the routing guide (Restricting the
Routes Created)to read "unused routes" instead of "unused routed" in the
link text.

Author: msducheminjr

guides/source/routing.md

@@ -1292,7 +1292,7 @@ In this case, Rails will create all of the normal routes except the route for `d
 TIP: If your application has many RESTful routes, using `:only` and `:except` to
 generate only the routes that you actually need can cut down on memory use and
 speed up the routing process by eliminating [unused
-routed](#listing-unused-routes).
+routes](#listing-unused-routes).
 
 ### Translated Paths