Change the minimum allowed message to 13d23h59m

Connection/API lag could cause messages right on the edge of 14 weeks to fail on Discord's end when they pass our checks.

src/Discord.Net.Core/Utils/Preconditions.cs

@@ -185,7 +185,7 @@ namespace Discord
         // Bulk Delete
         public static void NoMessageOlderThanTwoWeeks(ulong[] collection, string name)
         {
-            var minimum = DateTimeUtils.ToSnowflake(DateTimeOffset.Now.Subtract(TimeSpan.FromDays(14)));
+            var minimum = DateTimeUtils.ToSnowflake(DateTimeOffset.Now.Subtract(TimeSpan.FromMilliseconds(1209540000)));
             for (var i = 0; i < collection.Length; i++)
                 if (collection[i] <= minimum) throw new ArgumentOutOfRangeException(name, "Messages must be younger than two weeks to delete.");
         }