Incorrect timestamp serialization on non-english locales

[snechaev]

Environment: Win10 with non-english locale. The decimal delmeter is comma (,)

Code snippet

            var client = new SlackTaskClient(token);
            var loginResult = await client.ConnectAsync();
            var chanell = client.Groups.First(x => x.name == "<private channel name here>");
            var startDate = DateTime.Now.Date - (new TimeSpan(1, 0, 0, 0));
            var endDate = DateTime.Now.Date;

            var history = await client.GetGroupHistoryAsync(chanell, endDate, startDate); //System.OverflowException

In last line I got System.OverflowException inside Json parser.

In the sniffer I see the following request parameters (note decimal delimiter)

latest=1552323600,000000
oldest=1552237200,000000

End the response (also note delimiter)
{"ok":true,"latest":"1552323600,000000","oldest":"1552237200,000000","messages":[],"has_more":false}

If I replace delimiter in the request with the period (.), all works fine.