fix: http download fail (#61)

ui/flutter/android/app/build.gradle

@@ -48,7 +48,7 @@ android {
         // You can update the following values to match your application needs.
         // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-build-configuration.
         minSdkVersion 19
-        targetSdkVersion flutter.targetSdkVersion
+        targetSdkVersion 29
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName
     }