Swift: Update to package manager 5.1

swift/Package.swift

@@ -1,5 +1,23 @@
+// swift-tools-version:5.1
+
 import PackageDescription
 
 let package = Package(
-    name: "GildedRose"
+    name: "GildedRose",
+    products: [
+        .library(
+            name: "GildedRose",
+            targets: ["GildedRose"]),
+    ],
+    targets: [
+        .target(
+            name: "GildedRose",
+            dependencies: []),
+        .target(
+            name: "GildedRoseApp",
+            dependencies: ["GildedRose"]),
+        .testTarget(
+            name: "GildedRoseTests",
+            dependencies: ["GildedRose"]),
+    ]
 )