Simplify Flatpak environment detection

Author: priahoud

src/main/kotlin/com/jetpackduba/gitnuro/App.kt

@@ -94,7 +94,7 @@ class App {
         val windowPlacement = appSettingsRepository.windowPlacement.toWindowPlacement
         val dirToOpen = getDirToOpen(args)
 
-        appEnvInfo.isFlatpak = args.contains("--flatpak")
+        appEnvInfo.isFlatpak = File("/.flatpak-info").exists()
         appStateManager.loadRepositoriesTabs()
 
         try {