Update Dependency on secp256k1.swift to Latest Version from Original Repo

Hey `BCSwiftCrypto` Maintainers,

First of all, thank you so much for all the work you've put into this package. I'm using it for BIP32 key derivation and BIP39 mnemonics and it's super helpful.
I also rely on [secp256k1.swift](https://github.com/GigaBitcoin/secp256k1.swift) and some of its latest features, which are not available in the version this package uses.
After some wrestling with SPM and read-only mode (sigh), I managed to swap the two and everything still worked, all test passing.
Would it be possible to update dependencies to the up to date (0.14.0) version of the actively maintained repo for `secp256k1.swift`? Might streamline things a bit and save me tons of patchwork.
Let me know if there is any way I can make myself useful :) Thank you!