Updating swift tools version to 5.5?

[news at helweg.eu]

Hi, 

I'm trying to implement the Wireguard iOS Kit into my own iOS App. I followed the description in the README.md of the wireguard-apple repo.

When I try to add the Swift-Package "https://git.zx2c4.com/wireguard-apple" xCode complains with: 

Invalid manifest (compiled with: ["/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc", "-vfsoverlay", "/var/folders/l6/dvt5060j6qlb9_cr_551vdpw0000gn/T/TemporaryDirectory.41wnnP/vfs.yaml", "-L", "/Applications/Xcode.app/Contents/PlugIns/IDESwiftPackageCore.framework/Versions/A/Frameworks/SwiftPM.framework/SharedSupport/ManifestAPI", "-lPackageDescription", "-Xlinker", "-rpath", "-Xlinker", "/Applications/Xcode.app/Contents/PlugIns/IDESwiftPackageCore.framework/Versions/A/Frameworks/SwiftPM.framework/SharedSupport/ManifestAPI", "-target", "arm64-apple-macos12.0", "-sdk", "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk", "-swift-version", "5", "-I", "/Applications/Xcode.app/Contents/PlugIns/IDESwiftPackageCore.framework/Versions/A/Frameworks/SwiftPM.framework/SharedSupport/ManifestAPI", "-sdk", "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk", "-package-description-version", "5.3.0", "-Xfrontend", "-serialize-diagnostics-path", "-Xfrontend", "/Users/jens/Library/Caches/org.swift.swiftpm/manifests/ManifestLoading/wireguard-apple.dia", "/Package.swift", "-disallow-use-new-driver", "-o", "/var/folders/l6/dvt5060j6qlb9_cr_551vdpw0000gn/T/TemporaryDirectory.mYqMCN/wireguard-apple-manifest"])

I can see that the iOS and macOS versions have been bumped to v12 and v15 in one of the last commits. 

Shouldn't the swift tools version also be updated to 5.5?  (First line in the Package.swift file).

Best, Jens