Update zeroize_derive (#2625)

## Issue Addressed

NA

## Proposed Changes

As `cargo audit` astutely pointed out, the version of `zeroize_derive` were were using had a vulnerability:

```
Crate:         zeroize_derive
Version:       1.1.0
Title:         `#[zeroize(drop)]` doesn't implement `Drop` for `enum`s
Date:          2021-09-24
ID:            RUSTSEC-2021-0115
URL:           https://rustsec.org/advisories/RUSTSEC-2021-0115
Solution:      Upgrade to >=1.2.0
```

This PR updates `zeroize` and `zeroize_derive` to appease `cargo audit`.

`tiny-bip39` was also updated to allow compile.

## Additional Info

I don't believe this vulnerability actually affected the Lighthouse code-base directly. However, `tiny-bip39` may have been affected which may have resulted in some uncleaned memory in Lighthouse. Whilst this is not ideal, it's not a major issue. Zeroization is a nice-to-have since it only protects from sophisticated attacks or attackers that already have a high level of access already.

crypto/eth2_key_derivation/Cargo.toml

@@ -8,7 +8,7 @@ edition = "2018"
 
 [dependencies]
 sha2 = "0.9.1"
-zeroize = { version = "1.1.1", features = ["zeroize_derive"] }
+zeroize = { version = "1.4.2", features = ["zeroize_derive"] }
 num-bigint-dig = { version = "0.6.0", features = ["zeroize"] }
 ring = "0.16.19"
 bls = { path = "../bls" }