Fixed interface implementation for StreamedCourse

#story[758]

visualiser/src/main/java/seng302/Mock/StreamedCourse.java

@@ -5,6 +5,7 @@ import seng302.Model.BoatInRace;
 import seng302.Model.Leg;
 import seng302.RaceDataSource;
 
+import java.time.ZonedDateTime;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
@@ -32,7 +33,7 @@ public class StreamedCourse implements RaceDataSource {
         return null;
     }
 
-    public GPSCoordinate getMark() {
+    public ZonedDateTime getZonedDateTime() {
         return null;
     }