Update Package.swift

Switch to Swift Package Manager dependency URLs that contain the .git extension. This is not required by SwiftPM, but if a project does not consistently use the .git extension on dependency URLs (or not) then SwiftPM can get into trouble. The majority of open source projects use or suggest using the .git extension, so this project will standardize in that direction as well.

Author: mattpolzin

Package.swift

@@ -17,7 +17,7 @@ let package = Package(
             targets: ["JSONAPITesting"])
     ],
     dependencies: [
-        .package(url: "https://github.com/mattpolzin/Poly", .upToNextMajor(from: "2.4.0")),
+        .package(url: "https://github.com/mattpolzin/Poly.git", .upToNextMajor(from: "2.4.0")),
     ],
     targets: [
         .target(