`cargo semver` fails, but doesn't print out useful information

[soenkehahn]

I'm running cargo semver on a project on this commit: https://github.com/soenkehahn/cradle/tree/afdaa20d206d728ed9bc1186c93c6740df0ef492. It prints out

    Updating crates.io index

And then exits with a non-zero exit code.

I've never used cargo semver before, but -- if it exits with a non-zero exit code -- shouldn't it at least print out some kind of error message?