Fix "no manifest" issue

 - Fix #37

Package.swift

@@ -1,26 +1,19 @@
 // swift-tools-version:5.0
 import PackageDescription
 
-// swift-tools-version:4.0
-
 let package = Package(
     name: "NXDrawKit",
     products: [
-        // Products define the executables and libraries produced by a package, and make them visible to other packages.
         .library(
             name: "NXDrawKit",
-            targets: ["NXDrawKit"]),
-    ],
-    dependencies: [
-        // Dependencies declare other packages that this package depends on.
-        // .package(url: /* package url */, from: "1.0.0"),
+            targets: ["NXDrawKit"]
+        )
     ],
     targets: [
-        // Targets are the basic building blocks of a package. A target defines a module or a test suite.
-        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
         .target(
             name: "NXDrawKit",
-            dependencies: [],
-	    path: "NXDrawKit/"),
-    ]
+            path: "NXDrawKit/"
+        )
+    ],
+    swiftLanguageVersions: [.v5]
 )