Cargo had a very rough bug recently that's been causing travis to fail for Rust projects:
https://github.com/rust-lang/cargo/issues/3340
But even after the fix landed, nightlies have been broken for a few days.
However,
It's fixed! 
2 Likes
Hmm, my rustup update got rustc 1.15.0-nightly (908dba0c9 2016-12-01) with cargo 0.16.0-nightly (3568be9 2016-11-26). Wonder why I didn't get 2016-12-02 like your travis build?
When I look at cargo-dist, the newest builds are dated 2016-11-28 02:32, and it's still that broken 3568be9.
But from the main dist, rust-nightly-x86_64-unknown-linux-gnu.tar.gz is dated 2016-11-29 20:19 yet contains the same cargo 0.16.0-nightly (built 2016-12-02) that you got in travis.
So, I guess this is in part a difference between how rustup.sh and rustup.rs perform the download, monolithic downloads versus componentized, and maybe there's some CDN oddness here too?