Add net5.0 target framework

src/Spectre.Console/Extensions/DayOfWeekExtensions.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Globalization;
+
+namespace Spectre.Console.Internal
+{
+    internal static class DayOfWeekExtensions
+    {
+        public static string GetAbbreviatedDayName(this DayOfWeek day, CultureInfo culture)
+        {
+            culture ??= CultureInfo.InvariantCulture;
+            return culture.DateTimeFormat
+                .GetAbbreviatedDayName(day)
+                .Capitalize(culture);
+        }
+
+        public static DayOfWeek GetNextWeekDay(this DayOfWeek day)
+        {
+            var next = (int)day + 1;
+            if (next > (int)DayOfWeek.Saturday)
+            {
+                return DayOfWeek.Sunday;
+            }
+
+            return (DayOfWeek)next;
+        }
+    }
+}