volo 0.3.3 released

[James Burke]

Available via `npm install volo`.

Fixes two issues:

* Some GitHub “Releases” URLs can be signed AWS URLs, and those only
allow GET requests, instead of HEAD requests.
* Some zip files are flatter, not all the contents are under a top
level directory.

Details of the bugs:
https://github.com/volojs/volo/issues?milestone=18&state=closed

James