add Sparkle appcast

Sources/iKeyMonApp.swift

@@ -12,7 +12,7 @@ import AppKit
 
 @main
 struct iKeyMonApp: App {
-    @StateObject private var updateViewModel = UpdateViewModel()
+    @StateObject private var sparkleUpdater = SparkleUpdater()
 
     init() {
         #if os(macOS)
@@ -25,7 +25,7 @@ struct iKeyMonApp: App {
     var body: some Scene {
         WindowGroup {
             MainView()
-                .environmentObject(updateViewModel)
+                .environmentObject(sparkleUpdater)
                 .onDisappear {
                     NSApp.terminate(nil)
                 }
@@ -35,7 +35,7 @@ struct iKeyMonApp: App {
         Settings {
             PreferencesView()
                 .padding()
-                .environmentObject(updateViewModel)
+                .environmentObject(sparkleUpdater)
         }
     }
 }