Fastfile: rename vi-VN to vi (for screenshots)

Author: tenzap

Diff for: fastlane/Fastfile

@@ -157,7 +157,7 @@ platform :android do
     capture_android_screenshots(
       use_timestamp_suffix: false,
       clear_previous_screenshots: true,
-      locales: ["en-US", "de-DE", "fr-FR", "pt-BR", "tr-TR", "vi-VN", "zh-CN"],
+      locales: ["en-US", "de-DE", "fr-FR", "pt-BR", "tr-TR", "vi", "zh-CN"],
       ending_locale: "en-US",
       reinstall_app: true,
       app_package_name: "com.exifthumbnailadder.app.debug",