Change field name

So that it matches the SetLevel4to5 implementation and doesn't cause back-compatibility issues.

Signed-off-by: Caspar de Haes <caspar.dehaes@five.ai>

osi_trafficupdate.proto

@@ -45,5 +45,5 @@ message TrafficUpdate
     // or vehicle category.  All dynamic fields should be populated where known,
     // for example, velocity, light states, or future trajectory.
     //
-    repeated MovingObject traffic = 3;
+    repeated MovingObject update = 3;
 }