Force defaults in aos_send

Otherwise with flatbuffer builds which don't have ForceDefaults set by
default, we end up not adding fields which have the default value.

Change-Id: Id9779f87995a0422ea6851abdfd5c919b26f63c4
diff --git a/aos/aos_send.cc b/aos/aos_send.cc
index d0dea01..d94418a 100644
--- a/aos/aos_send.cc
+++ b/aos/aos_send.cc
@@ -39,6 +39,7 @@
       cli_info.event_loop->MakeRawSender(channel);
   flatbuffers::FlatBufferBuilder fbb(sender->fbb_allocator()->size(),
                                      sender->fbb_allocator());
+  fbb.ForceDefaults(true);
   fbb.Finish(aos::JsonToFlatbuffer(std::string_view(argv[1]), channel->schema(),
                                    &fbb));
   sender->Send(fbb.GetSize());