message: Fix build on macOS (and C++17 compliance) (lib)
diff: @@ -1530,7 +1530,7 @@ error Context::downloadUpdate() {
  kDownloadStatusStarted);
  }
  - std::auto_ptr<std::istream> stream(
  + std::unique_ptr<std::istream> stream(
  Poco::URIStreamOpener::defaultOpener().open(uri));
  Poco::FileOutputStream fos(file, std::ios::binary);
  Poco::StreamCopier::copyStream(*stream.get(), fos);
  