message: Make exampleCustom.cpp work
  Did this ever work? Without this change I get an exception [here](https://github.com/arangodb/velocypack/blob/27d5366b995ad5931418cabeb3b364ace2d8b176/src/Dumper.cpp#L543).
diff: @@ -90,15 +90,15 @@ int main(int, char* []) {
  // now print 'custom1':
  std::cout << "'custom1': byteSize: " << s.get("custom1").byteSize()
  - << ", JSON: " << s.get("custom1").toJson() << std::endl;
  + << ", JSON: " << s.get("custom1").toJson(&options) << std::endl;
  // and 'custom2':
  std::cout << "'custom2': byteSize: " << s.get("custom2").byteSize()
  - << ", JSON: " << s.get("custom2").toJson() << std::endl;
  + << ", JSON: " << s.get("custom2").toJson(&options) << std::endl;
  // and 'custom3':
  std::cout << "'custom3': byteSize: " << s.get("custom3").byteSize()
  - << ", JSON: " << s.get("custom3").toJson() << std::endl;
  + << ", JSON: " << s.get("custom3").toJson(&options) << std::endl;
  VELOCYPACK_GLOBAL_EXCEPTION_CATCH
  }
  