Gummiboot: Switch to zip archive.

For some reason tarballs from cgit have a different hash each time you download.
Merge commit 'refs/top-bases/experimental/parallel-building' into experimental/parallel-building

# By Shea Levy
# Via Shea Levy
* commit 'refs/top-bases/experimental/parallel-building':
  Gummiboot: Switch to zip archive.