Use GitHub's `archive` URL for SHA1

To compensate for
https://github.com/mxcl/homebrew/commit/174acd649c19dbc83f34a6a9e95bdc137b1a2a1b,
we need to use the archive URL, rather than the tarball one so that we
calculate the correct SHA1 when generating the Homebrew formula.
Merge pull request #377 from stevenharman/use_archive_in_homebrew_task

Use GitHub's `archive` URL for SHA1

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