Update to fix Period Filter

Fixed issue with DataItem Period Filter. It was still comparing based on Unix Milliseconds as opposed to the new Unix Ticks format

src/MTConnect.NET-Common/Agents/MTConnectAgent.cs

@@ -758,7 +758,7 @@ private static bool FilterPeriod(IDataItem dataItem, long newTimestamp, long exi
                                 var period = TimeSpan.FromSeconds(filter.Value);
 
                                 // Get Duration between newTimestamp and existingTimestamp
-                                var duration = TimeSpan.FromMilliseconds(newTimestamp - existingTimestamp);
+                                var duration = TimeSpan.FromTicks(newTimestamp - existingTimestamp);
 
                                 return duration > period;
                             }