Lower the deployment target to macOS 10.15

Author: kinoroy

Package.swift

@@ -5,7 +5,7 @@ import PackageDescription
 
 let package = Package(
     name: "LibFido2Swift",
-    platforms: [.macOS(.v13)],
+    platforms: [.macOS(.v10_15)],
     products: [
         // Products define the executables and libraries a package produces, making them visible to other packages.
         .library(