fix platforms in Package.swift

Author: ngoleo

Package.swift

@@ -4,14 +4,14 @@ import PackageDescription
 
 let package = Package(
     name: "Nantes",
+    platforms: [.iOS(.v8)],
     products: [
         .library(name: "Nantes", targets: ["Nantes"])
     ],
     dependencies: [],
     targets: [
         .target(
             name: "Nantes",
-            platforms: [.iOS(.v8)],
             path: "Source/Classes",
             exclude: ["Nantes.h"]
         )