traces leaking user paths

Hi, we're using this crate indirectly in https://github.com/anoma/anoma via tendermint-rs and ibc-rs together with eyre error reporting. It seems that the traces included from here include user paths, e.g.:

```
The application panicked (crashed).
Message: called `Result::unwrap()` on an `Err` value:
0: HTTP error
1: error trying to connect: tcp connect error: Connection refused (os error 111)

Location:
/home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/flex-error-0.4.4/src/tracer_impl/eyre.rs:10
```

These paths seem to be compiled into release builds too. Could we possibly strip the prefix before the `.cargo` dir?