add expiry parameter

app/controllers/wiki_pages_controller.rb

@@ -31,7 +31,7 @@ class WikiPagesController < ApplicationController
       end
       format.json do
         render json: @wiki_pages.to_json
-        expires_in 7.days
+        expires_in params[:expiry].to_i.days if params[:expiry]
       end
     end
   end