Made EpochTIme internal

src/Discord.Net/Helpers/EpochTime.cs

@@ -2,7 +2,7 @@
 
 namespace Discord.Helpers
 {
-    public class EpochTime
+    internal class EpochTime
 	{
 		private static readonly DateTime epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
 		public static ulong GetMilliseconds() => (ulong)(DateTime.UtcNow - epoch).TotalMilliseconds;