We're having cargo trouble on rust-num/num#243, and it appears to be a new regression in the nightly. Note the initial Travis build succeeded, which was using cargo 0.16.0-nightly (b26d672 2016-11-25). Then several homu builds have all failed using cargo 0.16.0-nightly (3568be9 2016-11-26).

$ cargo build --verbose
    Updating registry `https://github.com/rust-lang/crates.io-index`
error: failed to load source for a dependency on `rand`
Caused by:
  Unable to update registry https://github.com/rust-lang/crates.io-index
Caused by:
  failed to fetch `https://github.com/rust-lang/crates.io-index`
Caused by:
  [16/-17] The SSL certificate is invalid

I confirmed the error locally after updating to the same cargo, running on Fedora 25.