Fix link to Roomba site

Update URL to point to current location of iRobot Create description

This p.r. points to the same page that the [artoo Roomba documentation](http://artoo.io/documentation/platforms/roomba/) links to from "+ info about the Roomba" button to be consistent (the current link results in a "page not found" error).

For reference, here is that most recent [Wayback Machine snapshot](https://web.archive.org/web/20130605070627/http://www.irobot.com/us/robots/Educators/Create.aspx) I could find of it.

Let me know if there is a different resource to point to and I'd be happy to update the commit. Cheers!