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/y2018/vision/vision.fbs b/y2018/vision/vision.fbs
index 14f8a45..5337f2b 100644
--- a/y2018/vision/vision.fbs
+++ b/y2018/vision/vision.fbs
@@ -2,8 +2,8 @@
 
 // Published on ".y2018.vision.vision_status"
 table VisionStatus {
-  high_frame_count:uint;
-  low_frame_count:uint;
+  high_frame_count:uint (id: 0);
+  low_frame_count:uint (id: 1);
 }
 
 root_type VisionStatus;