xyz@0.4.0

This [upgrade][1] brings two improvements:

  - we now specify the repository URL, so we no longer rely on `origin` pointing to __cheeriojs/cheerio__ (in my case, at least, it doesn't); and

  - xyz now aborts if the working directory contains unstaged changes.


[1]: https://github.com/davidchambers/xyz/compare/v0.3.0...v0.4.0