Moved up an item on systems design exercises.

README.md

@@ -971,9 +971,9 @@ You'll get more graph practice in Skiena's book (see Books section below) and th
         - Exercises:
             - Design a CDN network: old article: http://repository.cmu.edu/cgi/viewcontent.cgi?article=2112&context=compsci
             - Design a random unique ID generation system: https://blog.twitter.com/2010/announcing-snowflake
+            - Design an online multiplayer card game: http://www.indieflashblog.com/how-to-create-an-asynchronous-multiplayer-game.html
             - Design a key-value database: http://www.slideshare.net/dvirsky/introduction-to-redis
             - Design a function to return the top k requests during past time interval: https://icmi.cs.ucsb.edu/research/tech_reports/reports/2005-23.pdf
-            - Design an online multiplayer card game: http://www.indieflashblog.com/how-to-create-an-asynchronous-multiplayer-game.html
             - Design a picture sharing system: http://highscalability.com/blog/2011/12/6/instagram-architecture-14-million-users-terabytes-of-photos.html
             - Design a recommendation system: http://ijcai13.org/files/tutorial_slides/td3.pdf
             - Design a URL-shortener system: copied from above: http://www.hiredintech.com/system-design/the-system-design-process/