1.9.1 - Widen pin on swift-crypto dependency

What's Changed

Widen pin on swift-crypto dependency by @btoms20 in #120

What?

Widens the supported swift-crypto range to include the 4+ series of releases.

Why?

1. Using swift-crypto 4.2.0 doesn’t seem to impact the building or tests
2. Allows for newer libraries that need swift-crypto 4+ tags to still use this library
3. This combined with mysql-kit widening its pin on swift-crypto would allow vapor users depending on fluent-mysql-driver to use the latest, and safest, swift-crypto versions.

This patch was released by @gwynne

Full Changelog: 1.9.0...1.9.1