Fix/textpacker utf16

This small fix generates valid UTF-16 characters. This helps in storing these strings into localStorage or other browser based storages that don't support invalid UTF-16 characters.

For a better description of the problem see https://github.com/ConradIrwin/unicode-dragon/blob/2d09e722219869392626974387c6554fd1bf0c19/README.md#details fixing this one in NodeJS