Update TimeTool.cs

[GeErghon]

Error creating a week instance at the beginning of the year, the start and end dates are wrong. Ex
DateTime moment = new DateTime (2019, 1, 2);
Console.WriteLine ("Date {0}:", moment.ToShortDateString ());
var w = new Week (moment);
Console.WriteLine ("Week: {0} {1} - {2}", w, w.FirstDayOfWeek.DayOfWeek, w.LastDayOfWeek.DayOfWeek);
// got: w / c 1 2019; 2019-01-01 - 2019-01-07 | 6.23: 59 Tuesday-Monday
// expecting: Week: w / c 1 2019; 2019-01-01 - 2019-01-05 Sunday-Saturday

[EvanMulawski]

@Giannoudis Do you have time to look at this and possibly push out a patch version? Just ran into this issue. Thanks!