Update images

gtfs-realtime/spec/en/reference.md

@@ -635,11 +635,11 @@ A `Modification` message replaces a span of n stop times (`num_stops_replaced`)
 The sequence of `new_stops` may be of arbitrary length. For example, 3 stops could be replaced by 2, 4, or 0 stops as the situation may require. 
 
 
-<img src="images/trip_modification.png" width=650px style="display: block; margin-left: auto; margin-right: auto;">
+![](images/trip_modification.png)
 An example showing the effect of a modification on a particular trip. This modification may also be applied to several other trips.
 
 
-<img src="images/propagated_delay.png" width=650px style="display: block; margin-left: auto; margin-right: auto;">
+![](images/propagated_delay.png)
 Propagated detour delays affect all stops following the end of a modification. If a trip has multiple modifications, the delays are accumulated.
 
 
@@ -658,8 +658,7 @@ Each `ReplacementStop` message acts as a template for generating a new stop time
 The `arrival_time` is calculated from a reference stop in the original trip, plus the offset in `travel_time_to_stop`. The `departure_time` always equals the `arrival_time`.
 The optional fields of [`stop_times.txt`](https://github.com/google/transit/blob/master/gtfs/spec/en/reference.md#stop_timestxt) in the GTFS-Static specification are all set to their default values.
 
-
-<img src="images/first_stop_reference.png" width=650px style="display: block; margin-left: auto; margin-right: auto;">
+![](images/first_stop_reference.png)
 If a modification affects the first stop of the trip, that stop also serves as the reference stop of the modification.