Extensions built with the latest version of 'wheel' will not show metadata.

In `wheel (0.31.0)` (released [Apr 1, 2018](http://pypi.python.org/pypi/wheel)), the metadata.json file was removed and the CLI uses this to get metadata.
Until the CLI is fixed, build extension wheels with `wheel (0.30.0)`

See https://github.com/pypa/wheel/issues/195