Add default DateTimeFormat to Enable-LogFile cmdlet

Author: dlwyatt

Commands/EnableLogFileCommand.cs

@@ -14,7 +14,7 @@ public class EnableLogFileCommand : PSCmdlet
         private LogFile inputObject;
         private string path;
         private StreamType streams = StreamType.All;
-        private string dateTimeFormat;
+        private string dateTimeFormat = "r";
 
         #region Parameters