doc: update lua-cjson ref link.

Author: leslie-tsang

README.markdown

@@ -1011,7 +1011,7 @@ The order in which these modules are added during configuration is important bec
 filtering chain determines the final output, for example. The correct adding order is shown above.
 
 * 3rd-party Lua libraries:
-	* [lua-cjson](http://www.kyne.com.au/~mark/software/lua-cjson.php)
+	* [lua-cjson](https://www.kyne.au/~mark/software/lua-cjson.php)
 
 * Applications:
 	* mysql: create database 'ngx_test', grant all privileges to user 'ngx_test', password is 'ngx_test'