[DAS2] Link to GAME XML schema

[Nomi Harris]

http://biodas.org/documents/das2/das2_get.html has a link to 
http://flybase.net/annot/gamexml.dtd.txt for GAME XML documentation.
This link should be changed to
http://flybase.bio.indiana.edu/annot/game.rng.txt

Thanks,
        Nomi