Unaffected crates are still flagged as vulnerabilities

[MF1-MS]

This was come across as the presence of crossbeam v0.2.12 causes cargo audit to fail, despite the only affected version being v0.4.0, see: https://github.com/RustSec/advisory-db/blob/master/crates/crossbeam/RUSTSEC-2018-0009.toml

From a brief look at the code it seems that unaffected_versions needs to be stripped out like patched_versions in db.rs

[tarcieri]

Well that's unfortunate. I'll try to get a quick fix out for this.

[MF1-MS]

Cracking, many thanks.