correct double quotes for interpolation in routing guide [ci_skip]

guides/source/routing.md

@@ -668,8 +668,8 @@ get '/stories/:name', to: redirect('/posts/%{name}')
 You can also provide a block to redirect, which receives the params and the request object:
 
 ```ruby
-get '/stories/:name', to: redirect {|params, req| '/posts/#{params[:name].pluralize}' }
-get '/stories', to: redirect {|p, req| '/posts/#{req.subdomain}' }
+get '/stories/:name', to: redirect {|params, req| "/posts/#{params[:name].pluralize}" }
+get '/stories', to: redirect {|p, req| "/posts/#{req.subdomain}" }
 ```
 
 Please note that this redirection is a 301 "Moved Permanently" redirect. Keep in mind that some web browsers or proxy servers will cache this type of redirect, making the old page inaccessible.