Backport PR #9925: Only make .tar.gz sdists when releasing

PEP 527, which was just accepted, says that there can only be one sdist per release. Tarballs are already the more common sdist format on PyPI, so let's go with that.

Signed-off-by: Thomas Kluyver <[e-mail]>

tools/toollib.py

@@ -18,7 +18,7 b" archive = '%s:%s' % (archive_user, archive_dir)"
 
 # Build commands
 # Source dists
-sdists = './setup.py sdist --formats=gztar,zip'
+sdists = './setup.py sdist --formats=gztar'
 # Binary dists
 def buildwheels():
     for py in ('2', '3'):