Update ring version due to vulnerability problem

[Rodolfo P A]

The actual version of the project is pointing to ring = "0.14.0" which has a dependency to spin = "0.5.0" and this version has a vulnerability problem.
https://github.com/jjyr/hdwallet/blob/master/Cargo.toml#L20

It's possible to update the ring to ring = "0.16.9" which is using the spin = "0.5.2"
https://github.com/briansmith/ring/blob/master/Cargo.toml#L307

error: Vulnerable crates found!

ID:	 RUSTSEC-2019-0013
Crate:	 spin
Version: 0.5.0
Date:	 2019-08-27
URL:	 https://github.com/mvdnes/spin-rs/issues/65
Title:	 Wrong memory orderings in RwLock potentially violates mutual exclusion
Solution: upgrade to: >= 0.5.2