Fix link to Roomba site

Update URL to point to current location of iRobot Create description

Based on the most recent snapshot of the current link from the [Wayback Machine entry](https://web.archive.org/web/20130605070627/http://www.irobot.com/us/robots/Educators/Create.aspx), the updated link in this pull request seemed closest to the original page (using the same image and a similar description).

There were a couple other links that might also be preferable:
http://www.irobot.com/About-iRobot/STEM.aspx
http://www.irobot.com/About-iRobot/STEM/Create-2.aspx
http://www.irobot.com/About-iRobot/STEM/Create-2/Projects.aspx

Let me know if there is a different resource to point to and I'd be happy to update the commit. Cheers!