Use explicit flatbuffer IDs in y2017 and newer.

Non-explicit ids are risky.  We've seen backwards incompatible
changes...

Change-Id: Id6ceebe031ac80430191f367635d0e951c3d2cbc
diff --git a/y2019/camera_log.fbs b/y2019/camera_log.fbs
index 0ef7c04..11faf2d 100644
--- a/y2019/camera_log.fbs
+++ b/y2019/camera_log.fbs
@@ -1,7 +1,7 @@
 namespace y2019;
 
 table CameraLog {
-  log:bool;
+  log:bool (id: 0);
 }
 
 root_type CameraLog;