cargo-careful: Build failure on rust-sfml: possibly newer version of crate `core`

via reddit: running cargo careful test on https://github.com/jeremyletang/rust-sfml seems to result in an error

error[E0460]: found possibly newer version of crate `core` which `link_cplusplus` depends on
--> /home/dew/projects/github/rust-sfml/src/lib.rs:50:1
|
50 | extern crate link_cplusplus;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: perhaps that crate needs to be recompiled?