My code generating only numbers

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Fare;

namespace DbFillerConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            var pattern = @"[a-z0-9]{3}";
            var conv = new Xeger(pattern);
            Console.WriteLine(conv.Generate());
            // result will something like 123, 324 or 938 without letters
            Console.ReadKey();
        }
    }
}