LT format should allow both NNNNN and LT-NNNNN

[Tara Eckhoff]

For Lithuania (LT) zip code format, it should allow both NNNNN and LT-NNNNN. As example, this JS postal code validation library that allows both formats https://github.com/Cimpress-MCP/postal-codes-js/blob/master/formats/LT.json