RUSTSEC-2020-0141 MvccRwLock allows data races & aliasing violations

Affected versions of this crate unconditionally implement Send/Sync for MvccRwLock. This can lead to data races when types that are either !Send or !Sync e.g. Rc, Arc are contained inside MvccRwLock and sent across thread boundaries. The data races can potentially lead to memory corruption as...