hadoop-0.20.2 no longer on mirrors, now in archives

I am attempting to update an old formula. In particular:

$ brew versions hadoop
0.20.2 git checkout d0efd9e Library/Formula/hadoop.rb

That old formula needed a one line update because the URL had changed and that tarball is now found in the archives. After the update (with the same md5) the install worked.

Note that this is my first attempt to contribute to homebrew and I may not have done this right. Or maybe I did: I applied this patch to d0efd9e and the changeset does show this as a one line change. If I am not following the right path for updating an old version, I'm happy to resubmit this pull request with some guidance.