[sheepdog] Changing github tree

[MORITA Kazutaka]

Hi all,

Fortunately, I got the github account 'sheepdog' one month ago.
I think of moving from
  git://github.com/collie/sheepdog.git
to
  git://github.com/sheepdog/sheepdog.git

Any opinions?  If there are no objections, I think it's a good idea to
change our repositry at the same time as we release 0.7.0.

Thanks,

Kazutaka